Field-Effect Transistor (FET) Protection

WARNING: This page is about a different car, the 2018 Ford Focus. 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 used by the GFM2 to monitor and control current flow to the damper valve solenoids. The Field-Effect Transistor (FET) protection strategy prevents module damage in the event of excessive current flow.

The GFM2 utilizes a Field-Effect Transistor (FET) protective circuit strategy for damper valve solenoid outputs. 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 GFM2 resets the Field-Effect Transistor (FET) circuit protection to allow the circuit to function. The next time a circuit deactivated by a Field-Effect Transistor (FET) protection event is activated, 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 GFM2 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). For example, 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, the short circuit DTC stored on the first failure cannot be cleared by a command to clear the continuous Diagnostic Trouble Codes (DTCs) the cause of the concern must be identified and repaired. The module does not allow this code to be cleared or the circuit restored to normal operation until a successful self-test proves the fault has been repaired. After the self-test has successfully completed (no on-demand DTCs present), DTC U1000:00 and the associated short circuit DTC automatically clear and normal circuit function returns.

If the number of short circuit fault events reach the third tolerance level, then Diagnostic Trouble Codes (DTCs) U1000:00 and U3000:49 set along with the associated short circuit DTC. DTC U3000:49 cannot be cleared and the module must be replaced after the short circuit is repaired and the GFM2 on-demand self test indicates the short circuit DTC is no longer present.