: ECM...or Possessed by the Devil?

02-05-09, 01:12 PM
I think my ECM has gone wonky.

Car started throwing codes about a week ago, I won't go into the trouble of listing them all here, probably about 10 different codes at different times. Then I started getting a "Rear Door Ajar" message pop up regularly, then "Check Tire Pressure" would come on and off.

All of a sudden it seems like some of my "personal preference" settings in the computer were changing without any input from me (no other drivers using the car either.) Horn beeps, or doesn't beep when locked/unlocked...interior lights sometimes won't shut off after locking the car.

Also had random starting problems, it would sometimes start then shut off after about 2 seconds. Then start and run perfectly.

The "best" was last night when I put the car in drive all the interior lights came on, then as I was driving the doors would automatically start to lock/unlock/lock/unlock... :bonkers: I ended up disconnecting the battery and the computer did seem to "reset" itself...somewhat...the haunted door lock stuff stopped but the check engine light came on the moment I put it in reverse.

Anyhow...took it to the dealer and...of course...no starting problems and they couldn't make sense of the codes displayed...they seemed random and if valid the car wouldn't have been able to even run. They did manage to experience the haunted lock syndrome during a test drive though. Their best guess is that the ECM is failing.

Question...if I pick up a reconditioned ECM, or one from the junk yard is it just going to be a "plug and play" thing, or will it have to go back to the dealer to be "reprogrammed" or something?

02-06-09, 05:50 PM
Typically the pcm has the VIN programmed in. Other words it's not a plug-n-play swap. I've seen some of the sites selling used pcm's who say they will do it for you. Also you'll probably have to do a security relearn. About a 30 min process and instruction should be with any pcm purchased. Having the latest GM calibration might be worthwhile... and lastly you'll probably have to do what's called a CASE relearn. The engine will probably run but may not properly detect misfires. CASE relearn corrects for slight differences in true crank angle zero and the mechanical zero. Takes a Tech 2 or equivalent scanner.
Did the dealer give you any of the codes? Codes starting with a P are powertrain related, those starting with a B are body computer related and many of the items you mentioned are body control functions.
I've probably exceded the my limit of knowledge but will add one last thing. Over in the trailvoy forum I've noticed "similar" problems and often the feedback is a failing ignition switch. Causes all kind of weird electrical issues. This falls into FWIW column.
This is a typical link. There's several within this forum but some of the description sounds like your situation
Good luck

02-07-09, 02:32 PM
I've got a code reader. The codes it throws have all been "P" codes...but they vary from time to time in what code actually comes up.

Right now the most common error coming up is "Lift Gate Ajar"...which comes on every time you hit a bump and would seem to indicate a loose connection somewhere. For the life of me I can't find any physical switch on the lift gate to check. Must be buried somewhere in the latch or something.

Today I was driving along a section of straight dry highway and the "Stability Control System" would engage on and off. I also had another bout of the possessed door lock syndrome.

02-07-09, 08:23 PM
Most code readers available to mortal man won't read body codes.
Does sound like an intermittant short/loose connection.

02-10-09, 08:46 AM
Most code readers available to mortal man won't read body codes.
Does sound like an intermittant short/loose connection.
See my post here

02-12-09, 10:00 AM
I dont believe the Engine PCM is in charge of those other things you are having issues with. That would be the BCM.

However, if you say it is throwing p codes also, that would be the engine pcm, which is odd.

I have those ecms in stock and can setup one stock with your vin for 100 bucks. They are brand new ecms. BUT i dont think that is your problem. You have a bad switch somewhere or short./ loose wire...