C1288

Anti-Lock Control - Traction Control and Stability Assist

Pinpoint Test O: DTC C1288

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 requires service, a new HCU (Hydraulic Control Unit) must be installed.

- DTC C1288 (Pressure Transducer Main/Primary Input Circuit Failure)- If during the ABS module self-test or normal operation a condition (such as a short or open circuit) occurs that causes the transducer signal to read above 1,710 kPa (248 psi) when other inputs indicate a non-pressurized system, DTC C1288 sets.

PINPOINT TEST O : DTC C1288

NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.

O1 MONITOR THE PCM BRAKE ON/OFF (BOO1) PID

- Connect the scan tool.

- Ignition ON.

- Enter the following diagnostic mode on the scan tool: DataLogger- PCM.

- Press and release the brake pedal while monitoring the BOO1 PID.

Does the PID switch to ON with the brake pedal pressed and then to OFF with the brake pedal released?

Yes
GO to O2.

No
RETRIEVE any PCM DTCs. REFER to Computers and Control Systems Information for non-communication DTCs and REFER to Information Bus for any communication DTCs.

O2 MONITOR THE ABS MODULE MASTER CYLINDER PRESSURE (MC_PRES) PID

NOTE: To obtain the most accurate reading, it is recommended to use a graph display for this PID.

NOTE: The initial pressure reading may be greater than 0. This is a normal condition. If the pedal is not pressed slowly, an initial spike may occur.

- Enter the following diagnostic mode on the scan tool: DataLogger- ABS Module.

- Monitoring the MC_PRESS PID, make a note of the initial master cylinder pressure.

- Steadily press and release the brake pedal while monitoring the MC_PRES PID.

Does the PID smoothly increase with firm pressure on the brake pedal and then smoothly decrease with the brake pedal released, without any spikes, and does the final pressure match the recorded pressure within 0.5 psi?

Yes
GO to O3.

No
GO to O4.

O3 ROAD TEST THE VEHICLE AND MONITOR THE ABS MODULE MC_PRES PID WHILE DRIVING THE VEHICLE

NOTE: To obtain the most accurate reading, it is recommended to use a graph display for this PID.

NOTE: The initial pressure reading may be greater than 0. This is a normal condition. If the pedal is not pressed slowly, an initial spike may occur.

- Enter the following diagnostic mode on the scan tool: DataLogger- ABS Module.

- Monitoring the MC_PRESS PID, make a note of the initial master cylinder pressure.

- Road test the vehicle and have an assistant monitor the MC_PRES PID.

Does the PID smoothly increase with firm pressure on the brake pedal and then smoothly decrease with the brake pedal released, without any spikes, and does the final pressure match the recorded pressure within 0.5 psi?

Yes
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test.

No
GO to O4.

O4 ISOLATE THE HCU (Hydraulic Control Unit)

- Install a new HCU (Hydraulic Control Unit). Refer to Hydraulic Control Unit (HCU) Service and Repair. Calibrate the ABS module. Follow the scan tool directions for the calibration procedure.

- Enter the following diagnostic mode on the scan tool: DataLogger- ABS Module.

- Monitoring the MC_PRESS PID, make a note of the initial master cylinder pressure.

- NOTE: To obtain the most accurate reading, it is recommended to use a graph display for this PID.

NOTE: The initial pressure reading may be greater than 0. This is a normal condition. If the pedal is not pressed slowly, an initial spike may occur.

Steadily press and release the brake pedal while monitoring the MC_PRES PID.


Does the PID smoothly increase with firm pressure on the brake pedal and then smoothly decrease with the brake pedal released, without any spikes, and does the final pressure match the recorded pressure within 0.5 psi?

Yes
The concern has been corrected. RETURN the vehicle to the customer.

No
INSTALL a new ABS module, REFER to Anti-Lock Brake System (ABS) Module Service and Repair. Using the scan tool, CARRY OUT the IVD Initialization sequence. CLEAR the DTCs. REPEAT the self-test with the brake pedal not applied.