PCM or Wire Failure? EGR p0405 - Chevy Impala Forums
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PCM or Wire Failure? EGR p0405

Hey everyone!
So I'm working on a 2001 Impala 3.4L. It had a p0405 code.

What I know so far:
Did some backprobe testing on the EGR connector. Pin E is reading 12v. Pin D is reading the 5v ref. Which is good, but on C (position signal to PCM) it would jump sporadically between .05 to .5v. Confirmed EGR is faulty. Plugged in a new EGR and now I'm getting a steady .79. Sweet, but here's the problem I noticed next...

Current Problem:
Running the car the .79v doesn't change (except maybe +/- .01v) regardless of throttle. So... checked pin A and I'm getting 0.0v. What confuses me is that I can take this wire on pin A, ground it and that .79v still doesn't change. Which means I'm unable to manually command EGR. I'm concerned that this will simply throw a p0401 or some similar code when the computer goes to test emissions. Has anyone else had this issue? Does anyone have a wire diagram for this car? I would like to check for continuity to the computer but I don't know which pin it goes to. And I believe the wires feed into the side of the harness which would make it difficult (if not impossible) to figure out which wire goes to which pin. Does this sound like a bad computer?

Any advice would be much appreciated!
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I went ahead and checked each wire blindly. Disconnected the computer and checked each pin in the EGR plug looking for continuity in the comp plugs. Found a connection for each pin so it looks like each wire check out. What this doesn't tell me is if there are any possible duplicates (if I had a short to another wire for example). However, I don't think it's likely. Installed the new EGR last night and I'm waiting for the emissions monitors to complete. I'm hoping I just overlooked something when trying to manually command EGR and that it's not the PCM. If anyone would like the reference here are the computer pins I found that are connected to the EGR with their corresponding letters.









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Update:
P0401 code has been triggered finally as expected. I don't think it's a blockage problem since the EGR valve isn't even being used. I'd hate to just throw money at it and put a new computer in it (especially since idk what Chevy will charge to finalize the programming).

What makes me hesitant is that regardless of what condition the computer is in I ought to be able to manually operate EGR using the voltage provided by the computer. Does anyone know how to safely test the B lead? I haven't found online what the value should be. I just know that if you ground the wrong wire for the EGR it will fry the computer. Goal is to confirm a fault not cause another one lol.
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Don't know about your issue but if you do need a new computer check with https://circuitboardmedics.com
First. I needed one for my Mercury and they saved me hundreds of dollars and the car was fine yet when I still had and traded it.
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Thanks KBZ. Seems like a good deal. I'll probably get a quote from them if I can confirm it's in fact the PCM.

I did manage to find some info on the B circuit. I unplugged the EGR. Probed B with one lead. With key on engine off touched the other lead to battery POSITIVE. In my case I found 12v which is what you want.

Unfortunately, since I've been able to confirm C, D and E are reading correctly this test was unnecessary as it's the ground for the sensor data.

What's still unknown is how to properly test the A circuit (the computer controlled ground). I'm pretty sure I ought to be able to command EGR with this wire.
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Update:

Did some more driving tests with voltmeter hooked up to to C (signal voltage). Surprisingly I noticed that my voltage would drop when accelerating. It would usually go to .6 something volts but at a couple points it would go as far as .5v. What in the world?
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