Engine 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 and the ECM grounds the EST line. It expects to see no activity on this line at this time. When the ECM enters EST mode, it applies +5 volts to the BYPASS line and expects to see voltage variations on the EST line.

Reasons for the ECM to set Code 42:

- System in BYPASS mode (i.E. EST line supposedly grounded) but activity sensed on EST line

- System in EST mode (i.E. BYPASS line driven with +5 volts) but no activity seen on the EST line

Possible causes include:

1) BYPASS line is open or grounded

2) EST line is open or grounded

3) Poor connections between ignition module and ECM

4) Poor routing of EST harness and/or poor quality ignition wires (EMI induced electrical noise

5) Faulty or incorrect ignition module

6) Faulty ECM