C0635

DTC C0635, C0638, C0640, C0643, C1252 or C1253





Circuit Description
The Continuously Variable Road Sensing Suspension (CVRSS) module estimates the road surface and communicates that information to the Electronic Brake Control Module (EBCM). The CVRSS module provides a Pulse Width Modulation (PWM) signal to the EBCM through the left and right normal force signal circuits. The CVRSS module sends each normal force value twice to the EBCM. The possible values of the PWM duty cycle are 20%, 40%, 60% and 80%, with the valid range from 10-90%. The EBCM uses this information to provide improved rough-road braking performance.

Conditions for Running the DTC
The ignition is ON.

Conditions for Setting the DTC
DTC C0635 or C0640
The DTC is set when the CVRSS module measures a feedback voltage less than a preset value during five consecutive normal force signal output OFF state tests.

DTC C0638 or C0643
The DTC is set when the CVRSS module measures a feedback voltage greater than a preset value during five consecutive normal force signal output ON state tests.

DTC C1252 or C1253
The DTC is set if one of the following conditions is present for 5 seconds of any 10 second period:
^ The PWM duty cycle is outside the valid range of 10-90%.
^ The PWM duty cycle value does not match either the previous or the next PWM duty cycle value.

Action Taken When the DTC Sets
^ Both the left and right normal force outputs are set to default output states.
^ The EBCM disables the rough road detection function for the duration of the ignition cycle.
^ The SERVICE RIDE SYS message will be displayed.

Conditions for Clearing the MIL/DTC
^ The scan tool can be used to clear the DTC.
^ The DTC is saved as history when the CVRSS module no longer sees an out of range feedback voltage during five consecutive normal force OFF states. The DTC will clear if the fault does not return after 50 consecutive ignition cycles.

Diagnostic Aids
^ The DTC may be caused by an open or a short in the normal force signal circuit.
^ The DTC may be caused by a poor connection at the EBCM or CVRSS module connectors.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. This step tests for a valid duty cycle in the normal force signal circuit.
3. This step tests for normal voltage in the normal force signal circuit.