Field Effect Transistor (FET) Protection

A Field Effect Transistor (FET) is a type of transistor that, when used with module software, monitors and controls current flow on module outputs. The FET protection strategy prevents module damage in the event of excessive current flow.

The BCM utilizes a FET protective circuit strategy for many of its outputs (such as a turn lamp output circuit). Output loads (current level) are monitored for excessive current (typically short circuits) and are shut down (turns off the voltage or ground provided by the module) when a fault event is detected. A short circuit DTC sets when the fault event occurs. The circuit remains off until the fault is corrected and the ignition is cycled off and then back on. The module then resets the FET protection and allows the circuit to function. After a preset number of retries with the short circuit present the output is shut down for all drive cycles until the fault is repaired, the related DTC is cleared and the BCM passes a self-test.

A module lifetime is established based upon the durability of the FET. If an output has reached the maximum number of activations the BCM sets DTC U3000:49. When DTC U3000:49 sets and the Diagnostic Trouble Codes (DTCs) are cleared the short circuit DTCs no longer sets to indicate the type of fault on the output circuit before permanent deactivation occurred. Once the number of short circuit fault events reach a predetermined maximum level, DTC U3000:49 cannot be cleared and the module must be replaced after the initial fault is repaired to return the associated functionality to the vehicle.