DTC 42

Fig. 049 - Chart - Code 42 Computer Controlled Coil Ignition:

Fig. 050 - Wiring Diagram for Code 42 Computer Controlled Coil Ignition. VIN 9:

Code 42 means the ECM has seen an open grounded bypass or EST circuit with the engine running.

1. and 5. Checks to see if ECM recognizes a problem. If it doesn't set code 42 at this point, it is an intermittent problem and could be due to a loose connection.
2. With the ECM disconnected the ohmmeter should be reading less than 200 ohms, which is normal resistence of the ignition module.
3. Checks to see if ignition module switches when the by pass circuit is energized by 12 volts through the test light. If the ignition module actually switches, the ohmmeter switches to over 8,000 ohms.
4. Disconnecting the ignition module should make the ohmmeter read as if it were seeing an open circuit. If the ohmmeter has a low reading, CKT 423 is shorted to ground.