Thank you for the detailed information you supplied and I applaud you for trying to diagnose the problem rather than just replacing parts.
The first thing I notice in the one picture you posted is that two terminals appear to be suspect - I have identified them with red arrows. The one at the end appears to have the tongue portion of the terminal pushed up a bit and it appears to have a darker colour where it would make contact with its counterpart which could be causing an intermittent connection and the one near the middle appears to have a bit of tarnish as well. It could just be the quality and angle of the photo that the connector was taken at but I would suggest verifying that they are good. I think the one at the end is the power feed for the module.

The other thing I noticed is the tests you made and I wonder if these were done with the connector unplugged and with no load placed on the circuits? I will attempt to point out things that may show your tests as good when there could still be a problem - not trying to criticize but educate.

I pulled out the multimeter and follow along with the Service Manual steps. By completing the following

• Test the Red/Wht B+ wire for Voltage: 12.5V - If this was done using a voltmeter connected to the connector and the connector was not plugged in then the reading may not really prove anything. To properly test the circuit would need to have a load placed on it with something like the module or a 12 volt lamp. I would suggest using a light bulb that can draw about an amp or two since the circuit is fused at 10 amps - even an incandescent test light may show up a problem but they usually only draw around 300 milliamps. Sometimes you can clip the test lead clip to the negative lead of the meter and hold it to the negative terminal of the connector. Then tough the positive lead to the Red/Wht B+ wire and observe the meter reading - let us assume that you get 12.5V. Then touch the probe of the test light to the positive lead of the meter and the light should light and then observe the meter reading - it should remain the same. If the voltage drops at all downward (such as 12.3V) then the circuit has a problem and there is excessive resistance somewhere in that circuit and as the current demand goes up (such as with the light bulb being lit) the voltage level is dropping. I am assuming that you used the ground terminal in the connector as your ground point for the measurement. You can also use a jumper wire and test bot the positive and negative portions of the circuit separately by connecting a jumper to a battery ground or positive terminal and then observe if there is any difference in the readings versus what you got at the connector terminals. If you obtain anything larger than 0.1 volts difference then there is a problem somewhere.
• 
  
• Test the 2 blk/wht ground wires for Continuity to negative post of battery: 1.1Ω (Service manual states under 10Ω is good) - what reading did you obtain with the meter leads connected together? 1.1 ohms may not seem like a lot but it is very difficult to use an ohmmeter to verify a circuit does not contain excessive resistance. Here is a link to a voltage drop article I wrote that may help you understand how testing for voltage drop is a much more effective way to determine if a circuit has excessive resistance. https://www.impalaforums.com/thread...ical-problems.1893448/?post_id=3749248&nested_view=1&sortby=oldest#post-3749248
• 
  
• Test the pink IGN wire for Voltage: 12v (When key is in run position) - That is a 0.5 volt difference compared with the 12.5V reading you got when you checked the hot at all times circuit which suggests there is a half volt of drop somewhere in that circuit. Again, was this test done with the circuit loaded or with the connector unplugged and where was the ground lead for the meter connected?

I hope this helps you a bit with your quest to finding the problem as I doubt the module itself is the problem but I may be wrong. Intermittent problems can be a challenge but life is full of them I have found over the years. One last thought would be to do a voltage drop test between the ground wires and a good known ground point such as the negative battery terminal to see what sort of reading you get with the circuit loaded - anything more than 0.01 volts would make me think that there could be excessive resistance and ground point can corrode over time.
One other thing I will mention is that dielectric grease can actually act as a insulator if too much is applied on a surface. I find a product called Fluid Film is better to protect terminals from corrosion - just a suggestion.
Forgot to mention that you can often back probe a wire terminal if you are careful using a thin strand of wire or a T pin if desired so that you can do checks using a meter or an oscilloscope to see what is actually happening in a circuit in real time without damaging the wire.

 

Thank you for the detailed information you supplied and I applaud you for trying to diagnose the problem rather than just replacing parts.
The first thing I notice in the one picture you posted is that two terminals appear to be suspect - I have identified them with red arrows. The one at the end appears to have the tongue portion of the terminal pushed up a bit and it appears to have a darker colour where it would make contact with its counterpart which could be causing an intermittent connection and the one near the middle appears to have a bit of tarnish as well. It could just be the quality and angle of the photo that the connector was taken at but I would suggest verifying that they are good. I think the one at the end is the power feed for the module.
View attachment 169708

The other thing I noticed is the tests you made and I wonder if these were done with the connector unplugged and with no load placed on the circuits? I will attempt to point out things that may show your tests as good when there could still be a problem - not trying to criticize but educate.

I pulled out the multimeter and follow along with the Service Manual steps. By completing the following

• Test the Red/Wht B+ wire for Voltage: 12.5V - If this was done using a voltmeter connected to the connector and the connector was not plugged in then the reading may not really prove anything. To properly test the circuit would need to have a load placed on it with something like the module or a 12 volt lamp. I would suggest using a light bulb that can draw about an amp or two since the circuit is fused at 10 amps - even an incandescent test light may show up a problem but they usually only draw around 300 milliamps. Sometimes you can clip the test lead clip to the negative lead of the meter and hold it to the negative terminal of the connector. Then tough the positive lead to the Red/Wht B+ wire and observe the meter reading - let us assume that you get 12.5V. Then touch the probe of the test light to the positive lead of the meter and the light should light and then observe the meter reading - it should remain the same. If the voltage drops at all downward (such as 12.3V) then the circuit has a problem and there is excessive resistance somewhere in that circuit and as the current demand goes up (such as with the light bulb being lit) the voltage level is dropping. I am assuming that you used the ground terminal in the connector as your ground point for the measurement. You can also use a jumper wire and test bot the positive and negative portions of the circuit separately by connecting a jumper to a battery ground or positive terminal and then observe if there is any difference in the readings versus what you got at the connector terminals. If you obtain anything larger than 0.1 volts difference then there is a problem somewhere.
• 
  
• Test the 2 blk/wht ground wires for Continuity to negative post of battery: 1.1Ω (Service manual states under 10Ω is good) - what reading did you obtain with the meter leads connected together? 1.1 ohms may not seem like a lot but it is very difficult to use an ohmmeter to verify a circuit does not contain excessive resistance. Here is a link to a voltage drop article I wrote that may help you understand how testing for voltage drop is a much more effective way to determine if a circuit has excessive resistance. https://www.impalaforums.com/thread...ical-problems.1893448/?post_id=3749248&nested_view=1&sortby=oldest#post-3749248
• 
  
• Test the pink IGN wire for Voltage: 12v (When key is in run position) - That is a 0.5 volt difference compared with the 12.5V reading you got when you checked the hot at all times circuit which suggests there is a half volt of drop somewhere in that circuit. Again, was this test done with the circuit loaded or with the connector unplugged and where was the ground lead for the meter connected?

I hope this helps you a bit with your quest to finding the problem as I doubt the module itself is the problem but I may be wrong. Intermittent problems can be a challenge but life is full of them I have found over the years. One last thought would be to do a voltage drop test between the ground wires and a good known ground point such as the negative battery terminal to see what sort of reading you get with the circuit loaded - anything more than 0.01 volts would make me think that there could be excessive resistance and ground point can corrode over time.
One other thing I will mention is that dielectric grease can actually act as a insulator if too much is applied on a surface. I find a product called Fluid Film is better to protect terminals from corrosion - just a suggestion.
Forgot to mention that you can often back probe a wire terminal if you are careful using a thin strand of wire or a T pin if desired so that you can do checks using a meter or an oscilloscope to see what is actually happening in a circuit in real time without damaging the wire.

Thanks for the detailed reply! I really appreciate your insight into electrical diagnosing as my knowledge on it is fairly limited. I definitely don't take your points as criticism and appreciate you educating me further on the subject.

To elaborate on a few points you've made.

1. Tarnish on Female end of connector pins.

-I noticed that as well, but I was confused as to where the male pins acutally make contact with the female pins. I had assumed that it would be in the outer cavities(Detailed with blue circle) so I presumed that the discoloration/tarnish on the inner cavities(Detailed with Black Circle) was the tang that held the pin in the connector and thought it would not affect the pin to pin contact.​

Never the less I understand that tarnish can cause excessive resistance so I went ahead an bought a pin tension / connection kit to verify measurements from inside of female pin. See kit I've purchased below off of amazon.​

​

​

2. How were tests completed

-All the tests were completed with the connector unplugged from the module and testing on the female end of the connector.​

​

3. Test for B+ circuit

- This test was completed by touching negative lead of Voltmeter to negative cable at the battery and the positive lead of the voltmeter was touched to the exposed pin in the female TCM connector. I do have a light tester and I will attempt to place it in line when testing to review if voltage drops at all. I will also test both negative and positive sides of the circuit with jumper wire as recommended. I'll update when I've completed these tests.​

​

4. Test for the 2 ground wire circuits in TCM connector

-This test was completed with having one lead of multimeter on the negative cable of battery and the other lead touching exposed pin in female TCM connector. I will have to double check what resistance measured with leads connected together, I can't remember off the top of my head while at work today. Thanks for the link to the article! I will review it today.​

​

5. Test for Pink Ignition circuit

- This test was completed by touching negative lead of Voltmeter to negative cable at the battery and the positive lead of the voltmeter was touched to the exposed pin in the female TCM connector. I did find it odd that the voltages were different however I assumed it wasn't an issue being that it was around 12V. Now I know this could be a telling sign. Thanks again. I'll test this circuit with the light meter attached in line as well to review any changes in voltage.​

​

Some other thoughts now that I have read through your response, What do you think of the Dark Blue ACC data wake up wire reading as only 11.3V? Seems like if voltage variation is an issue then this circuit has the most resistance somewhere inline.

Thanks for the tip on dielectric grease, I wasn't aware that it was insulating either. I had only applied a small amount to the face of the female connector. I will look into the fluid film product.
As for back probing, I was hesitant to do this as I thought I might damage the insulation of the wire, I see the connector has a wire stay on the back, would you recommend I remove this prior to back probing? (Circled in red)

 

The male pins do go in the outer cavities but it is imperative that the connection points where they mate with the terminals are clean and also that the terminals have some "drag" (or clamping action) on the pins so that there is always good conductivity and minimal resistance - resistance creates heat which can promote tarnish and weaken the terminal metals spring tension.
The wire stay should not have to be removed as often you can see the terminal where the wire is crimped on the back side - as long as the wire or pin is thin enough you can usually slide it in to make contact with the terminal metal. Sometimes it takes a gentle action and a little luck along with a couple of tries to get it to make contact.

The wake up reading at 11.3 volts would not be a concern to me at this point since it is probably coming from a serial data signal on a Bus line. That voltage you are seeing may be an average of a high / low waveform of serial data packets and it may not be a steady voltage such as what the module needs to work properly. To view the wakeup signal I would suggest using an oscilloscope which you probably do not have access to. I would concentrate on making sure the module has the proper voltage and ground circuits (powers and grounds) so the module is alive and able to do its job properly regardless of the system voltage of the vehicle. Something to keep in the back of your mind is that a vehicle electrical circuit is usually between 12.4 (at rest and everything shut down) and 14.2 volts (when the engine is running and the alternator is working properly). When the vehicle is starting and the engine is cranking over the starter current draw may actually lower the voltage of the vehicle electrical system to about 10.0 volts or slightly less depending on ambient temperature, condition of battery and circuits and this is when the power and ground connections to any module become critical so that they all still are alive so they can do their jobs and communicate with each other properly. Any excessive resistance can result in the 10.0 volt level that a module might see when cranking dropping below a threshold where the module temporarily looses its brain so to speak. Any tarnish or corrosion may result in the module voltage remaining below what it requires once the cranking engine starts and the system voltage recovers to normal levels - especially where moisture is present since electricity takes the path of least resistance and water is a much better conductor than air as far as resistance goes. Hope this makes sense to you.

 

Thanks again, all makes sense. I'm starting to lean more towards improper pin tension being the culprit. Being that this connector is mounted on the front of the trans and there are quite a lot of vibrations transferred to the connector it seems like the most likely cause. Either that or the tarnish that you mentioned. More to come once the pin tension kit arrives

 

So I went out to buy a better new multimeter with a bit more accuracy to retest the power/ground circuits Here were my results.

Prior to retesting I had removed both negative and positive battery cables and cleaned both with wire brush. I also cleaned the ground strap to the core support and the ground strap to the trans stud with a wire brush. Just to verify there wasn't any corrosion causing a bad ground.

This was tested again by removing the female TCM connector and testing it on the face of the connector.

For the 2 ground wires
First testing two multimeter leads together 0 Ω
-Ground Pin 1 to grounding stud on transmission: 0Ω
-Ground Pin 18 to grounding stud on transmission: 0Ω
-Ground Pin 1 to ground pin 18: 0Ω

Then for the B+ Always on Wire
-B+ pin 10 to Ground pin 1: 12.48V
-B+ pin 10 to Ground pin 18: 12.49V
-I tested the B+ wire with a test light in the circuit and no voltage drop occurred.

Testing the Pink IGN hot wire
-IGN pin 13 to Ground pin 1: 12.11V
-IGN pin 13 to Ground pin 18: 12.12V
-IGN pin 13 to Ground stud on trans: 12.12
-I tested with the test light in the circuit and no voltage drop occurred.

Testing the Dark Blue Accessory Data Wake Up wire
-Acc pin 15 to Ground pin 1: 11.41V
-Acc pin 15 to Ground pin 18: 11.41V
-Acc pin 15 to Ground stud on Trans: 11.41V

I am waiting for the pin tension kit to be delivered and I'm going to check that all the pins in the female connector have proper tension & test power and ground through the pin itself.
If all that checks out I will likely buy a refurbished TCM and swap it.
Fingers crossed to hoping its just a pin that has lost tension or is corroded creating high resistance.

 

The 12.12 volt reading on the ignition wire versus 12.48 volts on the B+ wire indicates there is a voltage drop of .36 volts at some connection point (or points) between the battery positive post and where the wire terminates at the TCM connector - to me this would be a concern as it indicates excessive resistance somewhere in that circuit. It may or may not be creating the problem with the TCM that you are experiencing but it will probably become a problem with the TCM or another module on that circuit at some point in the future. I would suggest that you measure the voltage drop between the transmission fuse (10 amp) and the positive battery post by placing the red meter lead on the battery post and the black meter on the fuse with the module plugged in and the key on - might need a jumper wire to connect to the positive battery terminal. If you have a wiring diagram for your car you can check and see how that circuit is fed from the positive battery post to the transmission fuse and then test at various points that are easy to get to so you can determine where the excessive resistance exists and then hopefully resolve the problem.

One other thing I would suggest is to actually measure how much the test light you used to do your tests actually draws for current when it lights - this can be done by connecting the test light and the amp meter portion of your multimeter in series and connecting the circuit to a 12 volt battery. If it is only drawing 200 or 300 milliamps my concern it is not loading or stressing the circuits you are testing enough to show up a voltage drop that may be present if the TCM module is drawing 3 or 4 amps which it can easily do in use.

 

One more suggestion would be to measure the voltage at the actual battery with the ignition on with your voltmeter to give you an idea of what the battery voltage is with a bit of load since the majority of modules will be powered on. Was also wondering if when you measured the B+ voltage at the TCM connector was the ignition on or off?

 

I had measured voltage from Battery and it was the same as the 12.48V on the B+ pins. I had measured B+ with the ignition off. I will test the voltage drop of the circuit in question.

 

Lin bus voltage looks ok as lin bus usually 1 volt less than battery voltage...Many modules on lin bus... Power steering assist has had many problems with wire rubs and shorting once and awhile.... You may have to trace the harness to trannie as wires are tight against it ....honey hole is under air scoupe for rubbing wires

 

Yeah I feel like it has to be somewhere where the wires are rubbing and causing a short, everything so far with it being intermittent points to a wiring issue. Are you saying that under the air box there is a location where wires rub?

 

General Update to track this issue down. I came back from a work trip for a couple of weeks and the Pin tension test kit arrived! I had went out and re-tested all the pins in the female connector similarly to my last test method this time looking to see if corrosion or pin tension was the culprit.

All the pin tension had good friction when tested so I ruled that out as a possible issue.

Testing voltages and ohms with the pin tester also showed good. Now the reading was from the internal portion of the female connector so more accurate to what would be seen on the male pins of the TCM. Here were the results which this time I followed the GM service guide. (See GM service guide snapshots below)

As a caveat, some of the voltages read lower because the car has been sitting and hasn't ran for a few weeks.

1. Test for less that 10 Ω between each ground circuit terminal and ground
-Ground Pin 1 to grounding stud on transmission: 0Ω
-Ground Pin 18 to grounding stud on transmission: 0Ω
-Ground Pin 1 to ground pin 18: 0Ω
2. Verify between each B+ Circuit terminal and Ground
-B+ pin 10 to Ground: 12.39V
3. Verify between ignition circuit terminal and ground
-IGN pin 13 to Ground: 11.76
4.Verify between the communication enable circuit terminal OR the accessory wakeup circuit terminal and ground.
-Acc pin 15 to Ground: 11.04V
5. Test for less that 130Ω between each pair of high speed GMLAN serial data circuits
-Pin 2 to Pin 12 of Data: 120.8Ω
-Pin 5 to Pin 14 of Data: 120.3Ω

After this I started the car up and NO MORE errors, Check engine light, etc. I was in shock. I thought at first maybe some corrosion on a female pin terminal that caused it. I called it a night and let the car sit over the weekend. I attempted to drive it around to verify about 4 days later and started it up. (Still good no lights!) Pulled it out of the driveway and headed down the road. I was diriving for about 5 minutes then when I was waiting at an intersection, BAM all the lights and errors pop back up and trans goes into limp mode. I head back home and about another 2 mins the lights go away and its good again.

At this point I'm not sure if there is a possibility that the TCM is faulty and causing the intermittent issue or if its the wiring somewhere in the harness that is wrecking havoc. The service guide leads to a replacement if all circuits test ok. Which they all have so far.

The car is now sitting back in the driveway with the errors. My plan is to retest, using the pin tension test kit to verify there isn't a break in a wire that I might be able to see now. Then I plan to complete the Voltage drop testing that 29 Chev has recommended. (Still need to wrap my head around it to execute) Edit: I found a good video to sum it up. I ended up purchasing the tool that the video recommended to easily test the circuits. (Skip to 6:20 to see the tool)

If nothing else the hail mary is to spend the cash on the TCM and see if that resolves it.

I'm determined to find the root cause to this issue and hopefully this thread will help document the steps for someone else in the future.

 

One other suggestion when doing the tests (voltage drop or ohm) is to wiggle / move the harness in numerous spots while observing the meter readings and see if you observe a change - if there is a break in one of the wires inside the harness this may help you locate it. Given the way that you described the problem it appears the problem is something that comes and goes fairly quickly which makes me think something is going open (wire, connection, etc.) (just for a millisecond sometimes) which will trigger the code and result in a loss of communication. Hope you find it.

 

Thanks! Good Suggestion, the tool arrives tomorrow so I will post what I find. The problem doesn't come an go quickly, I would say there are times when it occurs for a few minutes or other time when the problem was present for days at a time.

 

What codes are now coming up ?.They may lead to which wires to check for rubbing aka intermittent... Harness running on top of trannie is a good honey hole of problems on many of these cars. Check wires closely do the wiggle test ...Take out of loom and check
Its free just your time

 

Same code for Loss of Transmission Communication. Ok I will take a look at the harness on the top of the trans, Thanks for the tip!

 

So after today we have more to discuss, of course further complicating the problem.

Today started by going out and verifying that the TCM fault was still present (and it was) I then proceed to disconnect the TCM connector and start testing across the various circuits using the new load test tool to test for voltage drop. Here were the results. I used the ground pins in the connector to verify there wasn't any high resistance in the ground wires to the TCM as well.

1. Verify between each B+ Circuit terminal and Ground (This test was performed with the key in the 'on' position in the car and using the pin test probes)
-B+ pin 10 to Ground pin 1 Test: (Before Load Test) 12.24V
-B+ pin 10 to Ground pin 1 Test: (Load Applied) 12.17V
Voltage drop of 0.07V
-B+ pin 10 to Ground pin 18 Test: (Before Load Test) 12.22V
-B+ pin 10 to Ground pin 18 Test: (Load Applied) 12.15V
Voltage drop of 0.07V
2. Verify between ignition circuit terminal and ground
-IGN pin 13 to Ground pin 18: (Before Load Test) 12.20V
-IGN pin 13 to Ground pin 18: (Load Applied) 12.10V
Voltage drop of 0.10V
3.Verify between the communication enable circuit terminal OR the accessory wakeup circuit terminal and ground.
-Acc pin 15 to Ground pin 18: (Before Load Test) 11.54V
-Acc pin 15 to Ground pin 18: (Load Applied) 11.15V
Voltage drop of 0.39V

Now at this point I figured I found my circuit in question! However I would like to check with you all if this voltage drop of 0.39V is a telling sign that there is an issue with the circuit or if this is normal for this accessory communication wake up signal.

Here is a video testing that circuit for visual reference.
Video for Voltage Drop of Acc Wake up Signal

So from this point I start to do what @29 Chev & @Impoor recommend with wiggling the wires to check for any change in reading. I first start at the connector to the TCM and pull back the loom and inspect and wiggle wires to check connection to pin. No change in reading so I move on. I start to unwrap where the TCM harness connects to the main harness and wiggle/squeeze to check, again no change in readings. I move along the harness that runs on top of the transmission and wiggle/ move it up and down all the way back to the firewall. No change in reading still. It was starting to get dark outside so I figure it time to clean up and head inside.
Before I do, I decided to plug the TCM connector back into the TCM and see what happens. VIOLA the gear selector circle is back and there is no code for communication error. At this point I'm very confused because I did nothing that altered anything besides move the harness around and even then I didn't see any reading change on the Voltmeter when checking for voltage drop.

Very confused I sat in the car and pondered my skills of being able to diagnose this issue. I thought maybe time to sell this car and rid my life of these electrical nightmares. Only after thinking that, I see the dash lights flicker and the car start to fade out. I try pulling the key out and its stuck in the ignition (Similarly to when you have the battery disconnected) I go outside and look at the wiring verifying I didn't mess anything up. I decide to unplug the TCM harness from the TCM and go back in the car to test turning the key to the 'ON' position. Now there are NO dash lights almost like the battery is dead!!
I check the voltage on the battery and see its at around 6V and dropping about 1V every 5 seconds! I removed the negative battery cable to prevent it draining completely and throw a trickle charger on it. I let it charge for a few mins and checked the battery while charging, it was around 12.8 -13V. I removed the trickle charger and checked the battery again with voltmeter and see it hold steady at 12.7V. Perplexed, I put the negative cable back on the battery and here the car come back to life. I ran to the interior of the car to pull the key out of the ignition then ran back to the battery to check the voltage. I see the voltage at 12.4 then 12 then 11.5 then 11V all in a mater of seconds! It was draining immediately right before my eyes. I pulled off the negative cable of the battery and left it to the side.

At this point, I believe this car wants to see me suffer.

My best guess when thinking about this is that somewhere in the harness that runs on top of the transmission is an issue and when I was wiggling / moving / squeezing I surfaced another issue which is causing a short circuit somewhere in the wiring. Knowing that its draining even when the key is out makes me this it is a constant hot wire that's shorted.

If you guys have any guidance please share. My patience is starting to run thin with this car and I am ready to jump ship and dump this thing! Haha (In actuality i really want to fix it but I think the car hates me)

The saga continues....

 

Because I can't call it quits yet I went back out side to see how much the draw was on the battery to cause it to discharge so quickly. I disconnected the negative battery cable and set my DVOM to amps and checked the amperage between the negative post of the battery and the negative battery cable. I had a reading of 3amps! Being that the battery is probably tired from not charging due to it sitting for weeks now, I'm pretty sure that 3A draw was draining it quick. I'll have to start going through and checking fuses tomorrow to see what was the issue.

 

Did you end up getting a new TCM.. What was your outcome?

 

Respectfully,
Look closer at your results for IGN pin 13 to Ground pin 18.
Address (fix) Acc pin 15 to Ground pin 18.

Then change your tactic.

First, do a conventional PARASITIC DRAIN test series. You need to get a FAST SNAPSHOT of ALL the under-hood fuse box circuits. The test sequence and fill-in forms I use are in my help files. Keep it simple. Don't get fancy. Do the basic investigation and write down observations for each.

IF YOU CANNOT IDENTIFY PARASITIC DRAIN WITH KEY OFF AND REMOVED, AND ALSO WITH KEY ON, THEN YOU ARE GUESSING AND ASSUMING AND HOPING TO STUMBLE INTO A MASSIVE FIX. NOT GONNA HAPPEN.

Get some structure pointed toward the obvious trouble that is masking: power is draining the battery right before your eyes.

Fix the probably two parasitic drains, and fix the probably one key-on power drain, and your battery will stabilize.

When battery voltage is proper and stable, the SENSOR ARRAY (12v and 5v circuits) gets adequate power to support all sensors and devices and modules. Of interest: the 5v array is converted from 12v so the lower the 12v falls below 12v the lower the converted 5v array falls below 5v. RIGHT NOW YOUR ELECTRICAL SYSTEM IS UNDER-VOLTAGE. THAT MEANS ITS OVER-AMPERAGE. THAT IS DANGEROUS AND IT CREATES PHANTOM READINGS AND CONFUSES MODULES.

Chase the power drains, both key-off parasitic and key-on.

My help files:
II
V

 

Thanks! Yeah I had not had any issue with parasitic drain until yesterday. The car actually sat for over two weeks in early July, I came back and was able to start it right up. The drain occurred was evident to me yesterday after messing with the harness that runs over the transmission. I plan to head out and today and test which circuit is causing parasitic drain.

Could you please elaborate on your point of: "Look closer at your results for IGN pin 13 to Ground pin 18." Are you saying the 0.1V drop is indicating an issue on that circuit as well?

Also I'm not sure if you linked the help files but I couldn't click on them.

 

^
Ii

Keeping this separate from my post a moment ago.

Also see post #2 in my help files and look into your vehicle's current/voltage sensor to prove that the module is triggering the alternator to deliver adequate power to maintain battery. If the sensor or its plug or its wires to vehicle are compromised then fix it. This condition might be being masked by other troubles.

The process of battery failure bounces around but eventually the physical battery cannot hold deep charge and one observable symptom is a battery that jumps from 3v to 12v on trickle charge for a short time, as you reported here earlier. It is commonly the case that this sensor system is failed. The alternator tests will read normal. But no recharge power is sent to battery. This compounds the voltage-amperage consequences mentioned earlier.

 

Scroll to bottom of Post #3 and tap the desired attachments themselves. There is also a fuse box layout sheet tobuse to check-off each fuse as it's pulled for inspection.

I listed the attachments at top of post for table of contents, but that's not active link.

 

The pin 15 test is what I would expect to see since the ACC line is actually serial data communication from what I have read - I think if you check your wiring diagram you will find that line connects to the BCM, ECM, CCM (chassis Module) and the TCM and transmits serial data between them using a series of highs (around 11.2 volts) and lows (0 volts) and if you looked at the signal with a scope it would be a non symmetrical square waveform. It is probably a very low current digital signal and using your load tester is dropping the voltage as the tester pulls it a bit closer to ground. Don't think that is your problem.
A voltage drop of 0.1 volts that you got when you tested pin 13 to ground is a problem - should not be that much as it is .03 volts higher than you got on the B+ test using the same ground (terminal 18). I would suggest checking the circuit from the battery positive terminal to that connection using your wiring diagram at easy access points where there is a connection point (fuse, terminal relay, switch, etc.) to see where the voltage is dropping. Use the power distribution wiring information to see how the current flows from the battery positive to get to pin 13 of the connector. Given the results of your B+ to the same ground point test (terminal 18) I would say the voltage drop is occurring in the positive portion of the ignition feed circuit somewhere - just my opinion. Note: this drop may actually be greater when the vehicle is running and in motion since the TCM is communicating with other modules and drawing more current than it would be using your tester.
You can also connect a jumper wire from the battery negative post (or terminal) to one terminal on your tester and connect the other terminal to your ground wire terminal 18 and use your voltmeter to determine how much voltage drop is occurring on the negative side of your circuit - just a suggestion.

If you check the bottom left of member GrizChev post he has a link to his help files. Hope this helps you.

 

Thanks again for the guidance. I will plan to test further in a bit.

 

Was IGN pin 13 to Ground pin 18 done after waiting for modules to sleep?

 

Results after today's testing.

Issue regarding the parasitic draw. Turns out that when I connected my voltmeter to the (-) Battery post and (-) Battery terminal there is a short 30sec window of amperage draw (I assume certain systems wake up and then shut back off) During my test yesterday I didn't have the Voltmeter connected long enough and i assumed the 3A draw was a short. Below is video of Amps dropping to 10mA after the 30 second window. See video for reference. So this is not an issue.
Video of Amp draw for first 30 sec

I had started testing before @29 Chev said that the ACC Wakeup Circuit reading is not the culprit. So I traced the ACC wire to the Harness connector between the engine and the Instrument Panel Harness (I/P) the connector is listed as X111 in the Service Manual. I tested with the voltage drop test at the I/P connector to test the circuit beyond the engine/trans harness to see if the same Voltage drop reading occurred.

Before testing I had the battery hooked to a charger which is why I assume the voltages are reading higher

For reference yesterday when testing, the Voltage drop for the ACC wire at the TCM was 0.39V shown by yellow line above.

Testing from Pin H (TCM ACC Wakeup) on I/P Connector to Ground. Shown by Blue line in diagram above
-Acc pin H to Ground: (Before Load Test) 12.26V
-Acc pin H to Ground: (Load Applied) 11.92V
Voltage drop of 0.34V

I then crossed checked with the other ACC Wakeup signal that goes to the ECM Pin D. Shown by Orange line in diagram above
-Acc pin D to Ground: (Before Load Test) 12.33V
-Acc pin D to Ground: (Load Applied) 11.98V
Voltage drop of 0.35V

Knowing that @29 Chev confirmed this was not an issue I can move on from that circuit.


Next is the IGN circuit that was a .1V Drop in yesterdays testing.

So the Voltage drop at Pin 13 to ground was 0.1V. tested at female end of TCM connector.

I tested the voltage drop at both side of the trans fuse (Shown by two pink arrows)
Both readings were the same at
-Trans Fuse to Ground: (Before Load Test) 12.72V
-Trans Fuse to Ground: (Load Applied) 12.61V
Voltage drop of 0.11V

My next steps will be to check Voltage at Relay Hot leads for that circuit.

 

Ref cool suggestion by @29 Chev

"You can also connect a jumper wire from the battery negative post (or terminal) to one terminal on your tester and connect the other terminal to your ground wire terminal 18 and use your voltmeter to determine how much voltage drop is occurring on the negative side of your circuit - just a suggestion."

Note that B- voltage drop up to 0.3v is acceptable in this sort of circuit. Anything connected thru a module needs time to sleep. Defined as all modules asleep.

I didn't see evidence in these circuits that simply metering would wake-up modules but the module circuits are black, and connections convoluted, and the 'master' module governing sleep is the last one to sleep. That can take ~20 minutes. So when possible test as B- voltage drop because that module would not likely raise beyond 0.3v after a 15~30 second momentary rise.

 

Keeping this reminder separate:

Test results are effected by battery voltage. As pressure drops, amperage rises.

Remember to occasionally run engine (alternator) or attach TRICKLE charger and allow time to reach static battery POS to NEG of 12.4v or more.

Disconnect any external charger or power source and allow time for modules to sleep before metering.

If you open a door or bump a remote button then the 'master' module will wake-up related other modules. It's a pita but it us what it is. Those related modules usually go back to sleep quickly. The 'master' takes time. The diagrams give likely hints - but much is black.

If your alarm senses a bump or contact with vehicle, then don't touch the body or door handles and put a thick blanket over fender as cushion. Or pull alarm fuse (most systems will not care).

 

Thought this might help you and others who read this thread understand the data signal voltage reading you are getting on pin 15 - found a youtube video that shows the type of signal that I would expect to see on the ACC wire terminal 15 if it was viewed using a scope. As you can see the waveform is going from just under 12 volts to 0 volts for very brief portions of time when data is being sent or received and in between the waveform remains high at just under 12 volts. Since a multimeter sampling rate is not fast enough to accurately catch and display such rapid changes of voltage levels and most of the time the voltage level is just under 12 volts the multimeter sampling rate averages the voltage level samples it sees and decides the voltage level in this circuit is just under 12 volts and that is what it displays (the 11.41 volts you obtained during yesterdays tests). The voltage level on this circuit is constantly swinging from 0 volts to just under 12 volts as the modules it is connected to communicate (jibber jabber as Eric O calls it) back and forth whenever the vehicle is in an awake state - the current level of these types of circuits is usually in the milliamps to keep power consumption on the "electrical grid of the vehicle" to a minimum to reduce load on the battery and alternator. As such if any external load (such as your tester) is connected to the circuit the voltage level will usually drop noticeably such as you observed. Hope this makes sense to you.

 

I remember the days of analog meters. Infinite definition. Some guys with oscilloscopes could dig deep fast. Elegant wave forms. No choppers. When digital came out most of us were unimpressed.

Today, circuit board manufacturing is in nano scale. Transistors and even relay coils and switches don't physically look like they did. They are 4 angstroms thick and built in a diffusion or epitaxy process in a wafer lab. A 2 angstrom gateway is by nature pressure sensitive, so if electrons flow thru the gateway their simple pressure pushes thru 2 angtroms thickness of atoms, and so flows down another circuit path. Boom. A relay your eyes cannot see. And it lives in the low milliamp range. It's astounding stuff.

I was fortunate to have an opportunity to run production machines in a custom wafer lab for Motorola and ON Semiconductor. Three years of math-heavy custom diffusion. Some were new development and circuit integrations (some very smart engineers made my work look good God bless them). Most were actual production sent to market including separate processing for gov stuff. Those were exciting days. When my 3 year stint was over (2016) I had an emotional crash from realizing I would likely never again work with people that smart and dedicated. But it was time for me to get back outside, I thrived in mines and powerhouses and factories. And that wafer experience gave me tools I still use every day EVEN RETIRED! And plus I have awesome memories.

 

Thanks for the info on communication networks. I figured the high speed data wires would do that but I didn't know that the wake up signal would do that as well. I assumed it was just power on to wake up the module Pins 2, 5, 12, 14 on diagram.

I went out again and tested what was recommended.

I first checked the Volt drop as recommended by @29 Chev by connecting leads to battery ground and pin 18. I had a reading of 0V across those.

For the fun of it I check Volt drop across the ECM/TCM fuse in the fuse box which supplies the power to the B+ Circuit.
-ECM/TCM Fuse to Ground: (Before Load Test) 12.68V
-ECM/TCM Fuse to Ground: (Load Applied) 12.64V
Voltage drop of 0.04V

I then turned the key to the ON position to activate the IGN relay and circuit.

Tested the IGN pin 13 from the TCM connector again to verify voltage drop
-TCM IGN Pin 13 to Ground: (Before Load Test) 12.38V
-TCM IGN Pin 13 to Ground: (Load Applied) 12.14V
Voltage drop of 0.24V

Then moved to the Trans Fuse in the fuse box which is the next point up on the circuit and tested volt drop
-Trans Fuse to Ground (Before Load Test) 12.34V
-Trans to Ground: (Load Applied) 11.98V
Voltage drop of 0.36V
Video of test Trans Fuse Voltage Drop Test

The only next point up on the circuit is the battery main that feeds the fuse box so i tested the red lead that comes from the battery to the fuse box.
-Fuse Box Main to Ground (Before Load Test) 12.34V
-Fuse Box Main to Ground: (Load Applied) 12.06V
Voltage drop of 0.28V
Volt Drop Video Fuse Box Main

Again stumped and now I'm not sure if my test methods are correct. I added videos you yall can verify.

At this point I'm wondering if its possible for the battery itself to be the culprit? The battery's date tag shows its around 3 years old. Anyone have any experiences with these electrical issues due to an older battery? I did bring the battery to an auto store and have them test it and they said it came back as good so i figured that wasn't the issue early on.

 

I would say you are getting close to finding the area of excessive resistance - a voltage drop of 0.28 volts using your tester is too much in my opinion. Can you post a picture of the battery positive terminal (where the cable connects to the positive post to the Fuse Box Main feed as there is probably another connection or two in between that is a problem or it may even be corrosion in the main feed wire.

 

Re video. Touch the stud post at fuse box and then compare to video where touched terminal. This may explain voltage drop, it's a joint, possibly micro-corroded. Or possibly the threaded post or the connecting terminal-eye is unexpectedly aluminum (does not conduct as well as some other materials).

 

I had gone through an used a wire brush to clean all positive leads and grounds across the car earlier this month.

 

Went back out, Here are the pictures.

I also retested the Voltage drop with the key OFF and the the car sitting for 30 min or so. I started with testing the voltage drop from negative battery cable to positive cable.

Ground lead on negative battery cable and positive lead on positive battery cable.
Before load 12.63
After Load 12.59
Drop 0.04V

Ground lead on negative battery cable and positive lead on Fuse Box Hot Lead cable.
Before load 12.63
After Load 12.59
Drop 0.04V

Video of Test

So it seems like the voltage drop testing while the key is off is quite different than when the key is ON. Not sure if this help solve anything though.