ABS/ASC- Road Speed Signal

ABS/ASC-Road Speed Signal:

The vehicle speed signal is provided by the ABS/ASC control module. The wheel speed sensor input is processed by the ABS and made available to the M5.2 control module as a digital square wave signal. The frequency of the signal is proportional to the speed of the vehicle.

The vehicle speed input signal is continuously monitored as part of the OBD II emission requirements. The control module monitors the plausibility of the speed input against engine RPM and load.

The M5.2 control module also monitors the signal for abrupt fluctuations in the signal frequency to "detect rough road surfaces" for the purpose of misfire detection plausibility.

If a malfunction occurs, the control module limits the maximum RPM of the engine and the Check Engine Lamp will illuminate when the criteria for OBD II monitoring are satisfied.