PCM Controlled Warning Lamps Diagnosis

Circuit Description
The PCM controlled lamps are powered through an ignition positive voltage feed fuse. The PCM commands the instrument panel cluster to turn ON the Check Gauges indicator by grounding the generator lamp control circuit.

Diagnostic Aids
A PCM controlled lamp ON at all times most likely indicates that a condition is present which requires the attention of the vehicle operator.

Check Gauges Lamp
The PCM will apply ground to the generator lamp control circuit if Ignition 1 voltage decreases to less than 10 volts. The PCM will remove ground from the generator lamp control circuit when Ignition 1 voltage increases to greater than 12 volts. If DTC P0560 is set, refer to DTC P0560 System Voltage. P0560

If the Check Gages lamp is illuminated and Ignition 1 voltage is not within specifications, refer to Charging System for diagnosis. The PCM Controlled Lamps diagnostic table only checks the integrity of the generator lamp control circuit wiring and the PCM output driver

If the Check Gages lamp is ON and the generator lamp control circuit is not grounded, any of the following conditions may be causing the Check Gauges lamp to be illuminated:
- High engine coolant temperature.
- Low oil pressure.

Check for the following conditions:
- Poor connection at the PCM.
Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

- Damaged harness
Inspect the wiring harness for damage. If the harness appears to be OK, disconnect the PCM and turn the ignition ON. Observe a voltmeter connected between the generator lamp control circuit and ground while moving connectors and wiring harnesses related to the I/R A change in voltage will indicate the location of the fault.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart.
3. Normally, ignition feed voltage should be present on the output control circuit with the PCM disconnected and the ignition turned ON.
4. Checks for a shorted component or a short to B+ on the output control circuit. Either condition would result in a measured current of over 1.5 amps. Also checks for a component that is going open while being operated, resulting in a measured current of 0 amps.
5. Checks for a faulty instrument cluster
16. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.