Normal Operation

The ABS module monitors the brake pressure transducer in combination with other brake inputs: wheel speed sensors, stoplamp switch from the PCM over the High Speed Controller Area Network (HS-CAN) bus and lateral accelerometer from the sensor cluster. The pressure transducer signal is used by the ABS module for various diagnostic routines as well as to determine system functionality. The pressure transducer is located inside the Hydraulic Control Unit (HCU) and can be monitored via the master cylinder pressure (MC_PRESS) PID. The PID should correlate closely with system hydraulic pressure. When the vehicle is at rest without input from the brake pedal, this PID value should be at or close to 0 kPa (0 psi). However, due to factors such as vehicle age or minor discrepancies in manufacturing, PID readings may have some variability. If the transducer signal reads above 620 kPa (90 psi) when other inputs indicate the system should not be pressurized, DTC C1288 will be set. If the transducer requires service, a new HCU  must be installed.

• DTC C1288 (Pressure Transducer Main/Primary Input Circuit Failure) - If during the ABS module self-test or normal operation the ABS module detects an open, a short to voltage or a short to ground in the transducer, DTC C1288 will be set. Also, if the transducer input does not match the information received from other sources, DTC C1288 will be set.

  This pinpoint test is intended to diagnose the following: 

• Brake pedal binding
• Air in the brake hydraulic system
• Fluid leak in the brake hydraulic system
• HS-CAN  bus
• Stoplamp switch
• HCU