The Powertrain Control Module (PCM) operates its output devices, such as solenoid valves, relays and indicator lights, by commanding a driver module. A driver module is an electronic switch that turns ON to complete the ground circuit and operate the 12 volt device. A Quad Driver Module operates 4 electronic switches for 4 output devices. There are 2 QDMs in the PCM. Each has a feedback circuit that detects an open or short circuit on an output device that it controls.
See Figure 1
- All relays should have 70-90 ohms resistance. All solenoids should have 22-42 ohms resistance.
- Turn the ignition switch ON and watch the lights on the instrument panel. The SERVICE ENGINE SOON and coolant temperature lights should turn ON , then the coolant temperature light should go out. If not, check the fuses, bulbs and ground circuits.
- Jumper terminals A and B on the ALDL. The cooling fan on the radiator should run.
- Remove the jumper wire, then start the engine and operate the vehicle as required to test the remaining components.