Hi guys,

I have reasons to believe I have a PCM connection problem on my 2004 MC SS SC.

Occasionnaly (2 or 3 times a week) these lights come on in the dash: battery, seat belts or air bag, parking brake and passlock.

At the same time, all gauges go down to 0 and come back up. Usually, all the lights go off after a few seconds. The car runs normally and always starts normally.

I had it scanned by a friend mechanic and there were a zillion codes in there so he cleared them all. Next time it happen I had it scanned immediately and there was half a dozen codes but the most interesting to me was U1016, lost connection with PCM.

I read here and elsewhere that most PCM problems are not with the unit but rather with the connection. I also read Chevrolet service bulletins that recommend to check the connections and use dielectric lubricant on the unit connection before replacing any module.

So I plan to disconnect my cars PCM, apply dielectric lubricant on the connections, and reconnect it.

But before I do that I need some advice:

Are there any necessary precautions (unplug the battery) before disconnecting the PCM ?

Are there any procedure required after disconnecting/reconnecting the PCM ?

What do you guys think of this procedure, is it usefull or useless ?

All opinions and advice welcome.

Thanks !

 

You could give it a shot, only need to disconnect the negative side. Be careful putting both connectors back in, get them lined up and don't over tighten the 7mm screws.

 

Definately worth a shot... Welcome to the forum... No relearn is necessary when connecting it back up, should fire right up... If that does not correct the problem(s), then I would reflash the PCM, if you do not have a custom tune ( if you do, just have the same person who tuned it do it again)... If that fails, I would try another pcm (flashed for your car) from a junk yard or sometimes members have them for sale here... If you can get a good scan afterwards, then it will just be an issue of chasing down the culprits... Good luck and keep us posted...

 

It's worth checking, see if there is corrosion on the connectors for the PCM. My guess is that all will be fine there (the connection has a gasket to weather seal it and the harnesses are bolted in).

The issues you describe make me suspect a BCM failure or a damaged wire.

Start with the check of the PCM connection. It costs nothing but a little time to ensure there is not a goofy issue at that spot.

 

I too was thinking BCM issues, as when mine failed it exhibited many of the same symptoms.

 

Makes perfect sense, didn't think of the BCM....

 

I've read here that the BCM can cause all the symptoms you spoke of except for all the CEL codes you found. I had a similar problem when I got my car. But my car was abused and neglected and stuck back together with Duct Tape and Chewing gum.
I say checking your PCM connector is a good start. I wouldn't discard a possible problem with the computer, but I would not place it on the top of my list. While you are in there though, i would check the wires at the connector to make sure they are seated correctly.

 

Thank you guys for the advice.

I will definitely turn my attention to the BCM.

So same questions:

Are there any necessary precautions before disconnecting the BCM ?

Are there any procedure required after disconnecting/reconnecting the BCM ?

Thanks again !

PS: I also found this (maybe you've seen it before) :

ww2.justanswer.com/uploads/heavychevy396/2010-11-23_110730_2000_chevrolet_impala_theft_relearn.pdf

PS2: The link does not work I don't know why. It will work if you copy/paste it in your URL field.

 

Anytime I work on the electrical system in a car I remove the neg battery terminal but some would say I'm paranoid. Better safe than sorry I say.
The BCM is located above the ebrake on the driver side. There will be 3 wire harnesses that connect to it: 2 grey (1 bigger than the other) and one pink. The BCM case itself has Grey Grey Pink in the plastic to tell you which one goes where.

You'll need to security relearn to get the car to start but several of the connivence features need to be dealer programmed to be fully operational.

When I looked at my similar issue last week amazon had a good deal on the replacement BCM. My issue was the gauges would go to 0, trac/abs would go off, low battery, low fuel, security and other lights would pop on the cluster and the radio would turn off. Mine wasn't a faulty BCM but rather a wire short in one of the splice packs under the steering column.

 

Another common cause of getting the U1016 (and the symptoms described) is a bad ground. You may want to clean it (under air box) and the battery ground (stud on transaxle) while you have the air box removed. Spray the PCM contacts down with electric motor cleaner before reassembly. A lot of the time people will conclude that the PCM is bad and replace it. It does solve the problem, but only because they reestablished a good ground when they put the new one in...