DTC 42

DTC 42 - Ignition Control (IC) Circuit:

Ignition Control Module Wiring Circuit:

Circuit Description:

The ignition control module sends a spark reference and a fuel control reference signal to the PCM when the engine is cranking. At the start of crank, the ignition control module controls ignition timing (module mode). When the PCM recognizes the second fuel control pulse, it sends a 5 volts signal on the bypass CKT 424 to switch timing to PCM control. An open or round in the IC or bypass circuit at the time the engine is started will set a DTC 42. The engine may be started but will run on module mode timing.
To set a DTC 42 the following conditions must be met:
^ Open or grounded CKT 423 at the time of engine start-up.
OR
^ PCM commanding bypass mode (open or grounded CKT 424) when the engine is started.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.
1. Checks to see if PCM recognizes a problem. If it does not set DTC 42, it is an intermittent problem and could be due to a loose connection.
2. With the PCM disconnected, the ohmmeter should be reading less than 200 Ohms, which is the normal resistance of the IC circuit through the ignition module. A higher resistance would indicate a fault in CKT 423, a poor ignition control module connection, or a faulty ignition control module.
3. If test light was "ON" when connected from 12 volts to PCM harness terminal "BC6", either CKT 424 is shorted to ground or the ignition control module is faulty.
4. Checks to see if ignition control module switches when the bypass circuit is energized by 12 volts through the test light. If the ignition control module switches, the ohmmeter reading should shift to over 6K Ohms.
5. Disconnecting the ignition control 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:
^ Poor Connection or Damaged Harness - Inspect PCM harness connectors for backed out terminals "BC6" or "BC7", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.
^ Intermittent Test - 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 change.
^ Detonation/Spark Knock/Pings