Normal Operation
The ABS module uses an internal solid state switch to operate the ABS pump motor. When the engine speed is above 700 RPM or the vehicle speed is at approximately 7 km/h (4 mph), the ABS module tests the ABS pump motor by activating it for 30 milliseconds. While the pump motor is being activated, the ABS module monitors the voltage drop across the ABS pump motor solid state switch and the amount of current the ABS pump motor draws through the solid state switch. If the voltage drop is too high or if the ABS pump motor is drawing too much current, the ABS module sets a DTC. After 30 milliseconds have passed, the ABS module stops applying voltage to the pump motor and observes the voltage that the spinning ABS pump motor is generating. The voltage generated by the motor indicates how fast the motor is spinning. A voltage that is too low indicates the motor is not spinning freely and a DTC sets.
When these DTCs set, the ABS module takes the following actions:
- ABS braking is disabled
- Traction control braking is disabled (although Engine Only Traction Control (EOTC) is still available)
- Stability assist is disabled
Fused battery voltage from Battery Junction Box (BJB) fuse 96 (50A) is used by the ABS module to power the ABS pump motor. Insufficient power or ground causes multiple DTCs to set.
- DTC C0020:15 (ABS Pump Motor Control: Circuit Short to Battery or Open) - sets when the ABS pump motor voltage feedback is greater than 0.75 volts for more than 50 milliseconds, if there is an open or high resistance on the ABS pump motor circuit between the ABS module and the Hydraulic Control Unit (HCU), or if the ABS module is faulted internally.
- DTC C0020:71 (ABS Pump Motor Control: Actuator Stuck) - sets when the ABS module detects that the ABS pump motor is not rotating when it is commanded to run.
This pinpoint test is intended to diagnose the following:
- Fuse(s)
- Wiring, terminals or connectors
- HCU
- ABS module