Code 42, Electronic Spark Timing (3.8L): Notes

Code 42 will set if EST or by-pass circuit is open or grounded at time of engine start-up.

1. Tests if ECM recognizes a problem. If ECM does not set Code 42 at this point, problem is intermittent. Check for a loose connection.
2. With ECM disconnected, digital volt-ohmmeter should indicate less than 200 ohms. This is normal EST circuit resistance through ignition module. A higher resistance would indicate a fault in circuit No. 423, a poor ignition module connection or a faulty ignition module.
3. If test light was on when connected from 12 volts to ECM harness by-pass circuit, either circuit No. 424 is shorted to ground or ignition module is faulty.
4. Tests if ignition module switches when by-pass circuit is energizedby 12 volts through test light. If ignition module switches, resistance reading should switch from less than 200 ohms to more than 6000 ohms.
5. Disconnecting ignition module should make ohmmeter indicate as if it were monitoring an open circuit (infinite reading). Otherwise, circuitNo. 423 is shorted to ground.