Circuit Description

The powertrain control module (PCM)/engine control module (ECM) controls most components with electronic switches which complete a ground circuit when turned on. These switches are arranged in groups of 4 and 7, and are called either a surface mounted quad driver module, which can independently control up to 4 output terminals or an Output Driver Module (ODM), which can independently control up to 7 outputs. Not all of outputs are always used.

Drivers are fault protected. If a relay or solenoid is shorted, has a very low or zero resistance, or if control side of circuit is shorted to voltage, it would allow too much current flow into PCM/ECM. The driver senses this, and output is either turned OFF or its internal resistance increases to limit current flow and protect PCM/ECM and driver. The result is high output terminal voltage when it should be low. If circuit from B+ to component or component is open, or control side of circuit is shorted to ground, terminal voltage will be low. Either of these conditions is considered to be a driver fault.

Drivers also have a fault line to indicate presence of a current fault to PCM/ECM s central processor. A scan tool displays status of driver fault lines as 0 = okay and 1 = Fault.