The Powertrain Control Module (PCM) 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 outputs (PCM) terminals or an output driver module, which can independently control up to 7 outputs. Not all outputs are always used.

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

When and output is ON, the terminal is grounded and the voltage will normally be low. When an output is OFF, the terminal voltage normally will be high.

Drivers also have a fault line in order to indicate the presence of a current fault to the PCMs central processor. A scan tool displays the status of the driver fault lines as 0 = OK, 1 = Fault.