Code 42 - Est Circuit Open Or Grounded (2.3L): Notes

Code 42 indicates ECM has seen an open or short to ground in HEI EST or by-pass circuit.

1. Checks if ECM recognizes a fault. If a Code 42 is not set here, an intermittent problem exists and could be caused by a loose connection.
2. With ECM disconnected, ohmmeter should indicate less than 500 ohms, which is normal resistance for ignition module. A higher resistance indicates a fault in circuit No. 423, poor ignition module connection or faulty ignition module.
3. If test light was illuminated when connected from 12 volts to ECM harness by-pass terminal, either circuit No. 423 is shorted to ground or ignition module is faulty.
4. Checks if ignition module switches when by-pass circuit is energized by 12 volts through test light. If ignition module switches, ohmmeter reading should switch from less than 500 ohms to greater than 8000 ohms.
5. Disconnecting ignition module should cause ohmmeter to indicate as if it were monitoring an open circuit (infinite reading). If ohmmeter indicates anything other than infinity, circuit No. 423 is shorted to ground.