Powertrain Controls - ECM/PCM

DTC 42 Ignition Control (IC) Error:

1X Signal Error:

CIRCUIT DESCRIPTION
The Electronic Ignition (EI) system module sends a reference signal to the Powertrain Control Module (PCM) when the engine is cranking. While the engine speed is under 400 RPM, the EI module controls the ignition timing. When the system is running on the ignition module (no voltage on the bypass line), the ignition module rounds the Ignition Control (IC) signal.

DTC 42 WILL SET WHEN
The PCM expects to sense no voltage on the Ignition Control (IC) line during this condition. If it senses a voltage, it sets DTC 42 and will not enter the ignition control mode.

When the engine speed exceeds 400 RPM, the PCM applies 5 volts to the bypass line to switch the timing to PCM control Ignition Control (IC). If the bypass line is open or grounded, once the RPM for ignition control is reached, the ignition module will not switch to Ignition Control (IC) mode. This results in low Ignition Control (IC) voltage and the setting of DTC 42. If the IC line is grounded, the ignition module will switch to Ignition Control (IC) but because the line is rounded, there will be no IC signal. A DTC 42 will be set.

ACTION WHEN (PCM WILL DEFAULT TO)
The PCM will turn "ON" the MIL (Malfunction Indicator Lamp).

DTC 42 WILL CLEAR WHEN
Conditions for fault are no longer present and Tech 1 "Clear DTCs" function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and fuse #9 is removed for 10 seconds.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. DTC 42 means the PCM has seen an open or short to ground in the IC or bypass circuits. This test confirms DTC 42 and that the fault causing the DTC is present.
2. Checks for a normal IC ground path through the ignition module. An IC CKT 423 shorted to ground will also read less than 500 ohms; however, this will be checked later.
3. As the test light voltage touches CKT 424, the module should switch. The actual reading on the J 39200 is not that critical as long as it does react when CKT 424 is triggered. The important thing is that the module "switched."
4. The module did not switch and this step checks for:
^ IC CKT 423 shorted to ground.
^ Bypass CKT 424 open.
^ Faulty ignition module connection or module.

5. Confirms that DTC 42 is a faulty PCM and not an intermittent in CKTs 423 or 424.

DIAGNOSTIC AIDS
If DTC 42 is intermittent, refer to Diagnosis By Symptom. Testing and Inspection