Code E042, Est Ignition Circuit: Notes

The C(3)I module sends a reference signal to the ECM when the engine is cranking. When the engine is running less than 400 RPM, the C(3)I module controls ignition timing. When the engine speed exceeds 400 RPM, the ECM sends a 5 volt signal on by-pass circuit No. 424 to switch timing to ECM control. An open or ground in the EST circuit will stall the engine and set a Code E042. The engine can be restarted but will run on module timing. The following conditions must be met to set a Code E042:

Engine speed greater than 600 RPM with no EST pulse for 200 milliseconds (open or grounded circuit No. 423)
ECM commanding by-pass mode (open or grounded circuit No. 424)

NOTE: Test numbers refer to test numbers on diagnostic chart.

Test Number 1) Checks to see if ECM recognizes a problem. If it does not set Code E042, it is an intermittent problem and could be due to a loose connection.

Test Number 2) With ECM disconnected, ohmmeter should be reading less than 200 ohms, which is the normal resistance of EST circuit through C(3)I module. A higher resistance would indicate a fault in circuit No. 423, poor C(3)I module connection, or faulty C(3)I module.

Test Number 3) If test light was on when connected from 12 volts to ECM harness terminal BC7, either circuit No. 424 is shorted to ground or C(3)I module is faulty.

Test Number 4) Checks to see if ignition module switches when by-pass circuit is energized by 12 volts through test light. If ignition module actually switches, ohmmeter reading should shift to greater than 6000 ohms.

Test Number 5) Unplugging ignition module should cause ohmmeter to read as if it were monitoring an open circuit (infinite reading). If not, circuit No. 423 is shorted to ground.