Field Effect Transistor (FET) Protection

WARNING: This page is about a different car, the 2016 Ford Transit Connect. However, it is still accessible from the selected car via links, so may be relevant.

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. The next time the driver requests a circuit to activate 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 shuts off the circuit again and the cumulative counter advances.

When the excessive circuit load occurs often enough, the module shuts down the output until a repair procedure is carried out. Each Field Effect Transistor (FET) protected circuit has 3 predefined levels of short circuit tolerance based on the harmful effect of each circuit fault on the Field Effect Transistor (FET) and the ability of the Field Effect Transistor (FET) to withstand it. A module lifetime level of fault events is established based upon the durability of the Field Effect Transistor (FET). If the total tolerance level is determined to be 600 fault events, the 3 predefined levels would be 200, 400 and 600 fault events.

When each tolerance level is reached, DTC U1000:00 should set along with the short circuit DTC that was stored on the first failure. These Diagnostic Trouble Codes (DTCs) cannot be cleared until the vehicle is repaired.

After the repair, it is necessary to clear the Diagnostic Trouble Codes (DTCs). Use the clear DTC operation on the diagnostic scan tool, cycle the ignition, and run the BCM on-demand self-test.

The module never resets the fault event counter to zero and continues to advance the fault event counter as short circuit fault events occur. If the number of short circuit fault events reach the third level, DTC U3000:49 sets along with the associated short circuit DTC. DTC U3000:49 cannot be cleared and the module must be replaced after the initial fault is repaired.