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Discussion Starter #1
Had a mental lapse and turned the car off with the AC running and fan set to high. The blower motor no longer works, at any speed. It worked fine at all speeds prior.

I picked up a replacement blower motor control module and it didn't fix the problem.

I've also checked the Battery #4 fuse, no avail.

Any other suggestions?
 

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Had a mental lapse and turned the car off with the AC running and fan set to high.
I don't think that should cause a problem. At least, I've never heard of turning it off first being required.

That said, I'd begin by testing the motor. Disconnect it from the motor control module and carefully jumper it to 12V. If the fan blows, then work your way upstream from there.

What year and model (gen8 or gen9) do you have? Basic HVAC or climate control?

There are 3 fuses which apply to the HVAC, as I recall. With the year info, I can look up a drawing for it.

HTH.
Doug

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Discussion Starter #3
Thanks for the reply Doug.
I have a 2012 (9th Gen) with basic hvac.
looks like I posted in the wrong forum...
I pulled the blower motor and will try to jump it soon.
 

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Discussion Starter #6
Reconnected the blower motor and wiggled the wires. Still no luck. Any possibility the fan speed knob went bad? How could I test that?
 

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I've attached a drawing for the motor control.

After BATT4, the other two fuses to check are DISPLAY and AIR BAG/DISPLAY. Both are in the underhood fuse box.

After those fuses,I think my next step would be to probe the blower control module. With the cable removed, ohm the black wire (pin A) to GND.

Next, you want to check the control signal, pin B. Ideally you need a scope for this, but I think an averaging meter will work. As you step the fan speed control, you should see the voltage step up.

After that, well...let us know what you find, and I'll try to come up with something else. That is, before concluding HVAC Control Module is bad, a couple more tests might be run to be sure.

HTH.

Doug

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2012 Impala, you say? Just spitballing here, but there were engine bay harness chafing issues in the 12's and 13's that are covered in this TSB.

TSB PI0631F

Blower motor operation isn't mentioned, but A/C pressure sensor is. Could this possibly be the cause of this problem too?
 
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Discussion Starter #9
I'm getting 8v on the main (red) wire. This stays wether the key is on or off.

Coming from the blower motor control modules (I tested the old and the new)
I'm getting 3 volts when the fan speed is set to off, and 0.3 volts when the fan speed is set to high. When the key is turned off, the voltage jumps back to 3v.
 

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I'm getting 8v on the main (red) wire. This stays wether the key is on or off.
It should be 12V (or greater) all the time. It comes straight from the battery thru fuse BATT4. So key-on or key-off won't matter. That it's measuring 8V is a concern. When you measure 8V, is the connector joined to the blower motor control module (BMCM)? That is, are you back probing the connector? Or is it disconnected when you measure 8V?

Coming from the blower motor control modules (I tested the old and the new) I'm getting 3 volts when the fan speed is set to off, and 0.3 volts when the fan speed is set to high. When the key is turned off, the voltage jumps back to 3v.
Looking at the drawing more closely, the HVAC control module is pulse width modulating the low side of signal 754, the GY/BK wire going to pin C of the BMCM. I'm thinking this is a logic signal, so it will switch between ~04.V and ~2.8V, which agree with your measurements of 0.3 and 3.0V

Since the low side is being driven (pulsed low), the lower the measured voltage is, the harder the fan is being driven. So your measurements of 0.3V on high, and 3V on off make sense to me. Can you get measurements at some intermediate speeds?

BTW, did you ohm out the black wire (pin A) to GND?

With the BMCM connected, you might try back probing pins E and D. Pin E should be at 12V, or in this case, 8V. And pin D should vary with fan speed setting, ~12V for off, and near 0 for high.

Given all this, I would focus on the 8V first. Make sure your meter is on a good GND, and take some underhood measurements. Remove fuse BATT4 and see what you measure feeding it. Then re-insert it. How does it feel goinig in? Is it snug or loose on either end? Then measure the voltage at connector X4, pin F1 of the underhood fuse box. Not sure how hard that's going to be to get at. But we need to figure out where the drop is between B+ and the 8V measured on the red wire (pin C) of the BMCM. The drop will be at a connection, most likely. Either at the fuse, or X4-F1, or at junction X210 in the drawing, etc. Find and fix this voltage drop, and you will probably be done.

Re: X210 - It's item 1 in the attached drawing. It's on the driver's side, left of the center dash section, above the floor hump.

HTH.
Doug

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Discussion Starter #11
Testing the fuse box...
On Batt 4 I'm getting 11.2 volts with both probes on the fuse pegs.
If I move the negative probe to a different ground, I get 12.4 volts.
 

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Testing the fuse box...
On Batt 4 I'm getting 11.2 volts with both probes on the fuse pegs.
If I move the negative probe to a different ground, I get 12.4 volts.
When you remove the fuse and insert the meter leads there, keep in mind, the low side of the fuse is not at GND - it's feeding the B+ pin on the blower motor control module. There's surely a little current going thru the meter into the BMCM with the result that there is a voltage across the BMCM, about 1.2V (12.4–11.2).

Doug

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Discussion Starter #13
Still trying to figure this out and coming up with dead ends..

The the blower motor 100% works
There is no change in results on the multimeter whether using the old blower motor control module or the new one.

I measure 11-12v when testing the red and black wires connected to the control module, however when I use a test light it doesn't show the red wire as Hot. Is this normal?
 

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Discussion Starter #14
Started noticing a hum/high pitched whining noise with the key on/engine off. When I pull the BCM fuse the noise goes away. Any thoughts?
 

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Still trying to figure this out and coming up with dead ends..

The the blower motor 100% works
You jumpered directly from B+ to the motor to verify this?

There is no change in results on the multimeter whether using the old blower motor control module or the new one.
So this indicates the problem is not in the BMCM.

I measure 11-12v when testing the red and black wires connected to the control module, however when I use a test light it doesn't show the red wire as Hot. Is this normal?
This may be a clue. A bad connection often behaves like a high resistance. So when you measured the voltage (between red and black), there is no current flowing except for a few micro- or nano-amps thru the meter. If your bad connection (somewhere in the path of the red wire and/or black wire) is 1000 ohms (for example), and your meter draws 1 micro-amp, the bad connection presents a voltage drop of 1 millivolt (= 1 micro-amp x 1000 ohms), a negligible amount.

Whereas, when you connect the test light, it draws a few milliamps or more. Say it draws 12milliamps. 12mA x 1000 ohms = 12V - ie, all the voltage is dropped across the resistance of the bad connection, preventing enough voltage from getting to the test light. (That's an over-simplification, but bear with me.)

Started noticing a hum/high pitched whining noise with the key on/engine off. When I pull the BCM fuse the noise goes away. Any thoughts?
I think this may be another good clue, the other being the aforementioned 8V measured on the red wire.

The problem is in one of these places:
  • path from BMCM pin A to GND
  • B+ path to BMCM pin C
  • path from BMCM pin E to motor
  • path from BMCM pin D to motor
  • signal path from HVAC CM to BMCM pin B
  • fan motor
Start with identifying a good GND point under the dash. The GND bolts under the dash are probably best. There are several of them. G200, shown in the schematic I posted, is #7 in the attached file. #2 and #3 are also GNDs.

Next, try to identify the source of the noise you heard. Crawl around under the dash listening for it. One thought I have on this is a failing motor. Sometimes, when they go bad, they will still run with full power applied. When you tested the motor, presumably with full voltage, the current flowing into it was sufficient to develop enough torque to get it running, enough torque to overcome any stiction inside the motor due to a bad bearing, for example.

But with the motor hooked up to the HVAC CM, perhaps there's not current flowing to get the motor started, so maybe the noise you hear is the hum of of a stalled motor.

Next, using the list below, take the measurements indicated in the attached drawing.
  • path resistance from BMCM pin A to GND (eg, G200)
  • B+ at the battery
  • B+ at X4-F1 at underhood fuse box
  • B+ at BMCM pin C
  • voltage at BMCM pin B
  • voltage at BMCM pin E
  • voltage at BMCM pin D
For the first one, you are verifying that the BMCM has a good GND. Use the meter to measure the resistance (ohms) between BMCM pin A and the GND at G200 (or whatever GND you have chosen). Take this measurement with IGNTION OFF. This should measure around 1 ohm or less.

Next, for the next 3 voltage measurements, with ignition on, for each one, step the HVAC control from OFF, to low, to hi, and log the measured voltages for each fan setting.

I'm thinking the problem is either in the GND path between the BMCM and GND, or between the battery and BMCM pin C. You measured 8V on the red wire at one point, which indicates a bad connection in the B+ path. (Keep in mind the previously posted drawing showing the location of X210 under the dash.) So if that is the case, it will show up in these measurements.

If there's a big difference between X4-F1 and BMCM-pinC, then the drop is probably in X210, the junction I mentioned previously, and included a drawing for the location. See earlier post.

After that, if the problem is still to be identified, for the final 3 voltage measurements, with ignition on, for each one, step the HVAC control from OFF, to low, TO LOW+1, to LOW+2,...to hi, and log the measured voltages. (For BMCM pins B, D and E). Here we are trying to identify if it's a problem with the HVAC CM or maybe the motor.

Let us know what you find.

Doug

[EDIT}Re: G200: Studying the attached drawing, I see that G200 appears to be a GND point on a wire, but not a GND bolt to sheet metal. So tracking it down to connect the meter lead is probably not helpful. Instead find a bolt anchored in sheet metal somewhere under the dash and use that for GND for measurements.

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Discussion Starter #16
Thank you for the help & guidance!
Finally got a new probe set so will try to get the results on the above tonight.

I've ruled out the blower (got a replacement and still no luck).
 

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Discussion Starter #17
Finally found the problem, while gethering the voltages. It was the power/ground (red & black) plug connector that is behind the glove box, before the blower motor control module. I had to remove the radio to access it. After pressing on the wires I saw the motor kick. Moving the wires around some more it fired right up. Thank you so much for all of your help!

You jumpered directly from B+ to the motor to verify this?

So this indicates the problem is not in the BMCM.

This may be a clue. A bad connection often behaves like a high resistance. So when you measured the voltage (between red and black), there is no current flowing except for a few micro- or nano-amps thru the meter. If your bad connection (somewhere in the path of the red wire and/or black wire) is 1000 ohms (for example), and your meter draws 1 micro-amp, the bad connection presents a voltage drop of 1 millivolt (= 1 micro-amp x 1000 ohms), a negligible amount.

Whereas, when you connect the test light, it draws a few milliamps or more. Say it draws 12milliamps. 12mA x 1000 ohms = 12V - ie, all the voltage is dropped across the resistance of the bad connection, preventing enough voltage from getting to the test light. (That's an over-simplification, but bear with me.)

I think this may be another good clue, the other being the aforementioned 8V measured on the red wire.

The problem is in one of these places:
  • path from BMCM pin A to GND
  • B+ path to BMCM pin C
  • path from BMCM pin E to motor
  • path from BMCM pin D to motor
  • signal path from HVAC CM to BMCM pin B
  • fan motor
Start with identifying a good GND point under the dash. The GND bolts under the dash are probably best. There are several of them. G200, shown in the schematic I posted, is #7 in the attached file. #2 and #3 are also GNDs.

Next, try to identify the source of the noise you heard. Crawl around under the dash listening for it. One thought I have on this is a failing motor. Sometimes, when they go bad, they will still run with full power applied. When you tested the motor, presumably with full voltage, the current flowing into it was sufficient to develop enough torque to get it running, enough torque to overcome any stiction inside the motor due to a bad bearing, for example.

But with the motor hooked up to the HVAC CM, perhaps there's not current flowing to get the motor started, so maybe the noise you hear is the hum of of a stalled motor.

Next, using the list below, take the measurements indicated in the attached drawing.
  • path resistance from BMCM pin A to GND (eg, G200)
  • B+ at the battery
  • B+ at X4-F1 at underhood fuse box
  • B+ at BMCM pin C
  • voltage at BMCM pin B
  • voltage at BMCM pin E
  • voltage at BMCM pin D
For the first one, you are verifying that the BMCM has a good GND. Use the meter to measure the resistance (ohms) between BMCM pin A and the GND at G200 (or whatever GND you have chosen). Take this measurement with IGNTION OFF. This should measure around 1 ohm or less.

Next, for the next 3 voltage measurements, with ignition on, for each one, step the HVAC control from OFF, to low, to hi, and log the measured voltages for each fan setting.

I'm thinking the problem is either in the GND path between the BMCM and GND, or between the battery and BMCM pin C. You measured 8V on the red wire at one point, which indicates a bad connection in the B+ path. (Keep in mind the previously posted drawing showing the location of X210 under the dash.) So if that is the case, it will show up in these measurements.

If there's a big difference between X4-F1 and BMCM-pinC, then the drop is probably in X210, the junction I mentioned previously, and included a drawing for the location. See earlier post.

After that, if the problem is still to be identified, for the final 3 voltage measurements, with ignition on, for each one, step the HVAC control from OFF, to low, TO LOW+1, to LOW+2,...to hi, and log the measured voltages. (For BMCM pins B, D and E). Here we are trying to identify if it's a problem with the HVAC CM or maybe the motor.

Let us know what you find.

Doug

[EDIT}Re: G200: Studying the attached drawing, I see that G200 appears to be a GND point on a wire, but not a GND bolt to sheet metal. So tracking it down to connect the meter lead is probably not helpful. Instead find a bolt anchored in sheet metal somewhere under the dash and use that for GND for measurements.

.



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