Code 42.....still runs

[milehighGN]

Hey guys. Getting a code 42........car still runs but feels very sluggish........checked grounds and ECM, everything looks "seated" properly. I figure it's the ignition module underneath the Coil pack.......anyone have any experience with these codes? Thanks!

[kenmosher]

Take a look here:

http://www.gnttype.org/techarea/ecmsensors/ecmpage.html

specifically:


http://www.gnttype.org/maint/malf.html


A code 42 says:

CODE 42

Trouble Code 42 indicates that there may be a malfunction in the Electronic Spark Timing (EST) system.

During cranking, the timing is controlled by the ignition module while the ECM monitors the engine speed. When the engine speed exceeds 400 RPM, the ECM sends a BYPASS signal to the ignition module which switches the timing to ECM control. The ECM calculates what the timing should be then "tells" the ignition module via the EST circuit.

An open or ground in the EST circuit will stall the engine and set a Code 42. The engine can be re-started but it will run on ignition module timing.

The conditions for setting this code are:


System in BYPASS mode but the ignition module is still controlling timing
- or -
Engine speed > 600 RPM with no EST pulses (ECM controlled timing) going to the ignition module for 200 msec.



Typical causes for this code include:

1) BYPASS line is open or grounded
2) EST line is open or grounded
3) PROM or CALPACK not seated properly in the ECM
4) Poor connections between ignition module and ECM
5) Poor routing of EST harness and/or poor quality ignition wires (EMI induced electrical noise)
6) Faulty or incorrect ignition module
7) Faulty ECM

[milehighGN]

Thank Ken. I've check that out, and it points to 7 different things...........just trying to see what other people's experience has been. I'm getting a new coil pack and ignition module, so that should clear it up. I don't know how the ECM could just go bad.

[Keller]

Use a battery charger lately? I've fried an ECM by using one before. I don't think the more modern ones are quite as brutal, but the older ones don't put out a very clean current.

A 42 is a hard one to diagnose. Resist just throwing your wallet at the problem.

[milehighGN]

If it still runs decently.......i've searched many posts saying the ignition module cleared it up. Plus mine looks original, and not super clean.