E042

Code E042 - C3-I EST or Bypass Circuit Failure:

Wiring Diagram for Code E042 - C3-I EST or Bypass Circuit Failure:

CODE E042 - C3-I EST OR BYPASS CIRCUIT FAILURE

Circuit Description:

The C3-I module sends a reference signal to the ECM when the engine is cranking. While the engine is under 400 RPM, the C3-I module controls the ignition timing. When the engine speed exceeds 400 RPM, the ECM sends a 5 volt signal on the By-pass circuit (424) to switch the timing to ECM control, through the EST circuit (423). An open or ground in the EST circuit will stall the engine and set a Code E042. The engine can be re-started but will run on module timing.

To set a Code E042 one of the following conditions must be met:

a. Engine speed greater than 600 RPM with no EST pulse for 200 msec. (Open or Grounded circuit 423) or
b. ECM commanding By-pass mode. (Open or Grounded circuit 424)




Test Description: The following numbered steps correspond with the step numbers on the diagnostic chart.

1. Checks to see if ECM recognizes a problem. If it doesn't set Code E042, 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 the normal resistance of the EST circuit through the C3I module. A higher resistance would indicate a fault in CKT 423, a poor C3-I module connection, or a faulty C3-I module.

3. If test light was on, when connected from 12 volts to ECM harness terminal "D5", either CKT 424 is shorted to ground, or the C3-I module is faulty.
4. Checks to see if C3-I module switches, when the bypass circuit is energized by 12 volts, through the test light. If the C3-I module actually switches, the ohmmeter reading should shift to over 8,0000 ohms. This verifies a complete CKT 424 and that CKT 423 is not shorted to ground.

5. Disconnecting the ignition module should make the ohmmeter read as if it were monitoring an open circuit (infinite reading). Otherwise, CKT 423 is shorted to ground.

Diagnostic Aids:

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Check For:

a. Poor Connection or Damaged Harness - Inspect ECM harness connectors for backed out terminals "B4" or "D5", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

b. Intermittent Test - If connections and harness check out ok, monitor a Digital Voltmeter connected from affected terminal to ground while moving related connectors and wiring harness. If the failure is induced, the voltage reading will abruptly changed.