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 Field Effect Transistor (FET) protection strategy prevents module damage in the event of excessive current flow.

The BCM utilizes a Field Effect Transistor (FET) protective circuit strategy for many of its outputs (for example, a headlamp 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 is stored at the fault event and a cumulative counter is started.

When the demand for the output is no longer present, the module resets the Field Effect Transistor (FET) circuit protection to allow the circuit to function once again. The next time the driver requests a circuit to activate (again, for example, the headlamps) that has been shut down by a previous short (Field Effect Transistor (FET) protection) and the circuit is still shorted, the Field Effect Transistor (FET) protection strategy again shuts off the circuit and increments the counter.

When the excessive circuit load / short occurs often enough, the BCM shuts down the specific circuit output. This occurs when certain programmed thresholds are reached, 1/3, 2/3, and 3/3 of the total tolerance level. In conjunction with the Field Effect Transistor (FET) shutdown, a DTC U1000:00 is set along with the short circuit DTC, for example B1D00:11. These Diagnostic Trouble Codes (DTCs) cannot be cleared until the shorted circuit is repaired.

After the repair of the shorted circuit it is mandatory to clear the Diagnostic Trouble Codes (DTCs) from the BCM so that it can reset the shut down Field Effect Transistor (FET) and function correctly again, Use the clear the Diagnostic Trouble Codes (DTCs) operation on the scan tool, then cycle the ignition, and re-run the BCM on-demand self-test. If the DTC U1000 and short circuit Diagnostic Trouble Codes (DTCs) are no longer shown than this indicates that the BCM has reset and the short has been repaired.

However, when the number of short circuit fault events reaches the final third level (3/3), DTCU3000:49 is set along with DTC U1000:00 and the associated short circuit DTC. DTC U3000:49 cannot be cleared and the BCM must be replaced after the initial fault is repaired.