Field-Effect Transistor (FET) Protection

The SJB  utilizes a Field-Effect Transistor (FET) protective circuit strategy for many of its outputs (for example, the headlamp output circuit). Output loads (current level) are monitored for excessive current (typically shorted circuits) and are shut down (turn off the voltage or ground provided by the module) when a fault is detected. A continuous DTC is stored at the time for the fault.

The circuit resets after a customer demand (ignition cycle) of the function (which switches the component on, causing the 30-minute battery saver timer to be energized). When an excessive circuit load (from a shorted circuit) occurs several times, the module shuts down the output until a repair procedure is carried out. At the same time, the continuous DTC that was stored by the first failure does not clear by a command to clear the continuous DTCs.

The SJB  does not allow the DTC to be cleared or the normal circuit function restored until a successful self-test (retrieving on-demand DTCs) proves that the fault has been repaired. After the self-test has successfully completed (no on-demand DTCs present), the continuous DTC clears and the normal circuit function returns.

The SJB  has 3 predefined levels of short circuit tolerance established. When the first or second level is reached, the continuous DTC associated with the short circuit sets along with DTC B106E. These DTCs (B106E and the DTC associated with the shorted circuit) may be cleared using the Clear DTC operation on the scan tool as long as the fault itself has been corrected. Each and every time the scan tool retrieves DTCs from the module and a circuit is shorted, a level of short circuit tolerance is used up.

If any of the circuits are shorted past the third level (if DTCs have been retrieved 3 successive times with the short circuit not having been repaired), then DTCs B106F and B1342 are set along with the associated continuous DTC. These DTCs (B106F and B1342) cannot be cleared and the module must be replaced.

The initial short circuit must be successfully repaired and its associated DTC cleared before the SJB  is replaced or the new SJB  may experience one or more of the short circuit tolerance levels being used up, causing a repeat replacement of the module.

DTC B106E sets when the SJB  has disabled a circuit due to a repetitive fault causing a circuit overload.