Chart C-16 PCM Controlled Warning Lamp Circuit

Chart C-16:

PCM Controlled Warning Lamp Circuit:

CIRCUIT DESCRIPTION
The "Temp" lamp or optional "Check Gauges" lamp, is connected to battery voltage through the ignition switch. The Powertrain Control Module (PCM) energizes the bulb by supplying a path to ground.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. This step checks for circuit 35 being shorted to ground or a faulty PCM.
2. This step checks the integrity of circuit 35. If circuit 35 is OK, jumpering PCM harness terminal "B8" to ground should illuminate the "Temp" / "Check Gauges" lamp.

DIAGNOSTIC AIDS
The engine coolant temperature sensor, in rare cases, may fail to indicate the correct engine coolant temperature without setting a Diagnostic Trouble Code (DTC). This could result in turning "ON" the "Temp" lamp or optional "Check Gauges" lamp without having an overheating condition. It could also result in overheating without the "Temp / Check Gauges" lamp being turned "ON." Vehicles equipped with the optional "UB3" gauges Instrument Panel (I/P) cluster utilize a "Check Gauges" warning lamp that indicates an overheating condition, low fuel level, low oil pressure, or low generator output.

An intermittent problem may be caused by a poor or corroded connection, rubbed through wire connection, a wire that is broken inside the insulation, or a corroded wire. Any circuitry, that is suspected as causing the intermittent complaint, should be thoroughly checked for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wiring connections, corroded terminals and / or wiring, or physical damage to the wiring harness.