Diagnosis in the Event of Signal Faults
Note. The ICM control unit itself contains sensors that provide the following signals: longitudinal acceleration lateral acceleration yaw rate. The wheel-speed signals are recorded and made available by the DSC control unit. The steering wheel angle is determined by the steering angle sensor in the steering column switch cluster. The ICM control unit processes all the sensor signals and makes these available in the form of bus signals to other systems in the vehicle. If fault code memory entries for these signals exist, the following procedure is recommended when working through the test schedules: Start with the test schedule for the control unit that is providing the signals. The most important signal sources for dynamic driving systems are the ICM, DSC and steering column switch cluster. You will be able to get to the root of the fault and eliminate it more quickly using this procedure. Instead, the test schedules for the control units that receive these signals only contain references to the transmitter control units which means they do not lead directly to the ultimate cause/solution of the fault.
Predrive test
Every time the engine is started or the vehicle is stopped, an automatic quick test of the hydraulic function of the failsafe valve and front-suspension pressure regulating valve is carried out which lasts only 450 ms and is imperceptible to the driver. That test is only started when the engine is running and the vehicle is stationary, provided no other fault is present. If the predrive test identifies a fault, the appropriate fault response is initiated.