Thread: 92 GP SE 3.1 Code 42 (ICM) 2 in a Row

Hello Everyone,

I recently purchased a 92 GP with 168k miles on it. While I am new to Grand Prix's, I have been working on cars as a hobby for the better part of 30 years (from ground-up restos to routine maintenance).

The first thing I did was replace a cracked vacuum line and decided to inspect the rest of the vacuum lines. One required removal of the battery as it goes underneath it, which means a computer re-learn process. After verifying all vacuum lines were good I put it all back together and ran it through the learning curve. When I got home it idled for about 5 minutes then just died and would not restart. Read the code and it was code 42 (ICM). Went and got a new ICM and disconnected the battery to clear codes while replacing it. Ran it through the learning process again and it ran good (mostly) for a couple of days, then died and would not start and gave code 42 again. Let it sit for a few days while doing other stuff, came back, still wouldn't start. Removed the battery for 10 minutes and it started right up. This time only lasted 1 day after learning process, and again code 42. Tried it all over again, just got back from a 40 mile trip where it acted pretty funky a lot of the time and code 42 again. (I should say that I always verified that there were no error codes before continuing each time).

Is it really possible that it could kill 2 ICM's in a row like that, or is there something else that might be causing this?

Already done:
Replaced the O2 sensor
Replaced the fuel pump relay
Replaced the ICM
Repaired all vacuum lines

The car has a 4 speed auto (not factory) with what feels like a converter lock in it also.

I could really use some help with this.

Thanks in advance for any input you might have

I would make sure your grounds are clean and tight. Especially anything near the battery. It's possible you might have bumped something over there when installing/removing the battery.

Thank you for the input Sven. I went out Monday and checked all the grounds and they are all good.

It occured to me that the Cranshaft Position Sensor (CKP) plugs directly into the ICM so I picked one up at NAPA for $20.99 on a chance guess. When I got home Monday I looked into which code a CKP would generate and there isn't one! As it turns out, in the 1989 1990 1991 1992 and 1993 Pontiac Grand Prix, code 42 is listed as "Ignition Control (IC) Circuit" which contains the Cranshaft Position Sensor.

I put in a new CKP and the code 42 went away.

I may have the same issue with my 92 SE also showing code 42. Could this also cause the Tach not to work?