PCM damaged by.....
Thread Starter
Joined: Sep 2004
Posts: 3,212
Likes: 1,613
From: Michigan & Florida
PCM damaged by..... I have a PCM from my '00 C5 that is acting weird. It throws a check engine light, BUT....NO CODE is set. I have been advised that this is one telltale indicator that the PCM is either damaged or junk. I also believe that, sometime in the recent past, I have seen some posts here, or read somewhere, that the engine should NEVER be cranked over without the spark plug wires plugged into the ignition coils. This situation did occur when I first got the motor in and tried cranking it over with the key to double check some of the wiring connections that were repaired and other issues. I just forgot about plugging the wires in to the coils. Does anyone know if this is, in fact, a no-no? And whether or not the check engine light being on, but no codes being set, means the PCM is bad? I have a second PCM- and when it is plugged in to the cars wiring harness, there is no check engine light-or codes. And I have the same tune in each unit. Thanks. 
Another issue I have seen a few times with the C5s is that the air conditioning condensation drains can get clogged up and cause the drainage to go directly on the PCM and cause damage to the PCM and corrode the harness... might be your problem. Did you see any signs that it may have gotten wet? It is also known to cause ground issues as well...
