•  The failure detection function detects malfunctions in the input/output signal systems of the 4-wheel drive (4WD) control module (CM) and displays them when the ignition switch is at the ON position.

•  When the ignition switch is turned to the ON position, the 4WD CM system begins operation, and the 4WD warning light illuminates for 3 seconds while the function checks for open circuits. At the same time the function monitors the condition of the power supply voltage and checks for internal malfunctions.

•  Then, once the system is running, the function checks the operating conditions of the 4WD solenoid and the differential oil temperature sensor at regular intervals to determine whether there is any malfunction.

•  If any malfunction is detected during these diagnostic tests, the warning light illuminates according to the malfunction to alert the driver. Also, a DTC is output to DLC-2 via the CAN line. Also, at the same time the failure detection result is sent to the memory and fail-safe functions.

•  This function stores DTCs for malfunctions of the input/output signal systems as determined by the failure detection function. Once a DTC is stored, it is not cleared even if the input/output signal system malfunction returns to normal when the ignition switch is turned to the LOCK position (engine OFF).

•  Since DTCs are stored in the non-volatile memory inside the 4WD CM, they are not cleared even if the battery is disconnected. Therefore, it is necessary to clear the memory when maintenance has been completed. For clearing DTCs, refer to the procedures in the Workshop Manual.

•  When the failure detection function determines that there is a malfunction, the 4WD warning light illuminates to alert the driver. At this time, the fail-safe function suspends control or takes other measures to ensure that driving stability is not lost.

•  This function allows for the storing and clearing of DTCs due to a communication link between the 4WD CM and an external tester.