ICM or ECM/ECU

[pitzel]

Ok, I am getting intermittent Code 42's, but with absolutely no other symptoms that are typically associated with coil or ICM failure such as misfires, bucking, stalling, rough running, etc. Searches of this forum seem to be equally divided on whether the problem usually originates from the ICM (Ignition control module), or from the main ECU/ECM.

 

Parts are expensive, and removing either the ECU or the ICM/coils is a huge nuisance.

 

Where should I start? Does off-car testing usually identify intermittent problems with ICM's? Anyone else had this happen?

[Crazy K]

I would first remove, inspect, clean, and di-electric grease all the contacts at the coil first to see if that makes a difference. might just be a poor connection?

[mfewtrail]

Have you read all the information pertaining to this code?

http://www.w-body.com/ecm-codes.html#42

 

If so, trace those bypass & EST wires to see if they're frayed and also check them w/ a mulitmeter for the proper operation mentioned on the code page. I can scan a page with the wiring information listed about this code...but my information is from a 1990 model repair manual(I'll try to compare 90 to 92 to see if they're the same if you do want that scan...).

 

EDIT: Here are the pages from my service manual for this code w/ a little more detailed info. I compared the wiring and it appears to be the same on the 3.1 Vin T cars at least until 1993(far as I checked). Tan/Blk at the ICM is the bypass wire, and the EST wire is white in color.

 

http://i44.photobucket.com/albums/f14/platjblser/IMG_1178.jpg (sorry about the darkness, I actually took this with my digi cam since my scanner is in my roommate's room @ the moment..didn't want to wake him up). Let me know if you can read/see those good enough.

 

& the diagnostic flowchart to go along w/ it,

http://i44.photobucket.com/albums/f14/platjblser/IMG_1181.jpg

 

Hope that helps.