Pinpoint Test G: DTC C1288
Anti-Lock Control
Pinpoint Tests
Pinpoint Test G: DTC C1288
Refer to Wiring Diagram Set 42, Vehicle Dynamic Systems for schematic and connector information. Diagrams By Number
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
PINPOINT TEST G: DTC C1288
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G1 CHECK FOR ACTIVE DTCs
- Connect the scan tool.
- Ignition ON.
- Using the scan tool, clear the ABS module DTCs.
- Enter the following diagnostic mode on the scan tool: Self-Test - ABS Module.
- Retrieve and record any ABS module DTCs.
- Is DTC C1288 present?
Yes
GO to G2.
For all other ABS module DTCs, GO to the ABS Module DTC Chart. ABS Module DTC Chart
No
The system is operating correctly at this time. TEST DRIVE the vehicle above 32 km/h (20 mph) and CARRY OUT at least one ABS stop. RETRIEVE and RECORD any DTCs.
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G2 CHECK THE OPERATION OF THE STOPLAMPS
- Apply the brake pedal and observe the stoplamps.
- Do the stoplamps illuminate when the brake pedal is applied?
Yes
GO to G3.
No
REFER to Brake Lamp to continue diagnosis of the stoplamp switch. Testing and Inspection
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G3 CHECK THE MASTER CYLINDER AND PEDAL FOR CORRECT OPERATION
- Press and release the brake pedal.
- Does the brake pedal smoothly travel to the stop and then return automatically when released?
Yes
GO to G4.
No
INSPECT the brake pedal and master cylinder for obstructions and foreign material that may cause a binding condition. REPAIR or INSTALL new as necessary. CLEAR the DTCs. REPEAT the self-test.
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G4 CHECK FOR AIR IN THE BRAKE HYDRAULIC SYSTEM
- Select PARK.
- Start the engine.
- Press and release the brake pedal several times.
- Does the brake pedal move smoothly and evenly through the length of its travel?
Yes
GO to G5.
No
REFER to Brakes and Traction Control to continue diagnosis of the brake hydraulic system. Testing and Inspection
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G5 CHECK FOR FLUID LEAKS IN THE BRAKE HYDRAULIC SYSTEM
- Visually inspect the brake hydraulic system for brake fluid leaks.
- Is the brake hydraulic system OK?
Yes
GO to G6.
No
REPAIR as necessary. BLEED the brake system. CLEAR the DTCs. REPEAT the self-test.
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G6 MONITOR THE PCM BRAKE ON/OFF (BOO) PID
- Enter the following diagnostic mode on the scan tool: DataLogger - PCM.
- Monitor the BOO PID while pressing and releasing the brake pedal.
- Does the PID agree with the brake pedal position?
Yes
GO to G7.
No
Using the scan tool, CARRY OUT the Key ON Engine Running (KOER) self-test. REFER to Computers and Control Systems Information to diagnose the DTC retrieved.
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G7 MONITOR THE ABS MODULE MASTER CYLINDER (MC_PRES) PRESSURE 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_PRES PID, make a note of the initial master cylinder pressure.
- Steadily press and release the brake pedal while monitoring the ABS module MC_PRES PID.
- Does the PID smoothly increase with increased brake pedal pressure and smoothly decrease with decreased brake pedal pressure, 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. TEST DRIVE the vehicle above 32 km/h (20 mph) and CARRY OUT at least one ABS stop. RETRIEVE and RECORD any DTCs.
No
INSTALL a new HCU. REFER to Hydraulic Control Unit (HCU) Service and Repair. CALIBRATE the ABS module. FOLLOW the scan tool directions for the IVD Initialization sequence. CLEAR the DTCs. CARRY OUT the self-test with the brake pedal not applied.
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