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uh oh code 42

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cyabye

New Member
Joined
Jan 5, 2002
Messages
26
I just recently purchased an 87 Turbo T from the original owner. The car runs and looks good and seems to be well taken care of. It has no modifications whatsoever, and all the maintenance has been taken care of by the Buick dealer. The check engine light is on, and upon scanning the computer, it revealed code 42. It has been my past experience with n/a cars that code 42 usually means bad module, ecm, or faulty wiring. I started off by replacing the module(original unit). No luck, the light is still on after clearing the code. Is the next logical step replacing the ecm? Or am I barking up the wrong tree? Any input would be greatly appreciated.
 
As per gnttype.org

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
 
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