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Pinpoint Test G: DTC C1288 - Pressure Transducer Main/Primary Input Circuit Failure

Refer to appropriate SYSTEM WIRING DIAGRAMS - EDGE or SYSTEM WIRING DIAGRAMS - MKX article, Vehicle Dynamic Systems for schematic and connector information.

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, 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.

This pinpoint test is intended to diagnose the following:

PINPOINT TEST G: DTC C1288 - PRESSURE TRANSDUCER MAIN/PRIMARY INPUT CIRCUIT FAILURE 

NOTE: Use the Flex Probe Kit for all test connections to prevent damage to the wiring terminals. Do not use standard multi-meter probes.
  1. G1 CHECK FOR ACTIVE DTCs 
    • Connect the diagnostic tool.
    • Key in ON position.
    • Using the scan tool, clear the ABS module DTCs.
    • Enter the following diagnostic mode on the diagnostic tool: Self-Test ABS Module
    • Retrieve and record any ABS module DTCs.
    • Is DTC C1288 present? 
    1. YES  : Go to  G2.

      For all other ABS module DTCs, go to the ABS MODULE DTC CHART  .

    2. 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.
  2. G2 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? 
    1. YES  : Go to  G3.
    2. 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.
  3. G3 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 it's travel? 
    1. YES  : Go to  G4.
    2. NO  : REFER to BRAKE SYSTEM - GENERAL INFORMATION article to continue diagnosis of the brake hydraulic system.
  4. G4 CHECK FOR FLUID LEAKS IN THE BRAKE HYDRAULIC SYSTEM 
    • Visually inspect the brake hydraulic system for brake fluid leaks.
    • Are any leaks found? 
    1. YES  : REPAIR as necessary. BLEED the brake system, REFER to BRAKE SYSTEM - GENERAL INFORMATION article. CLEAR the DTCs. REPEAT the self-test.
    2. NO  : Go to  G5.
  5. G5 MONITOR THE ABS MODULE BRAKE ON/OFF (BOO_ABS) PID 
    • Enter the following diagnostic mode on the diagnostic tool: DataLogger PCM
    • Monitor the BOO_ABS PID while pressing and releasing the brake pedal.
    • Does the PID agree with the brake pedal position? 
    1. YES  : Go to  G7.
    2. NO  : Go to  G6.
  6. G6 MONITOR THE PCM BRAKE ON/OFF (BOO) PID 
    • Enter the following diagnostic mode on the diagnostic tool: DataLogger PCM
    • Monitor the BOO PID while pressing and releasing the brake pedal.
    • Does the PID agree with the brake pedal position? 
    1. YES  : REFER to MODULE COMMUNICATIONS NETWORK article to diagnose the HS-CAN bus.
    2. NO  : REFER to EXTERIOR LIGHTING article to continue diagnosis of the BOO switch.
  7. G7 MONITOR THE ABS MODULE MASTER CYLINDER (MC_PRESS) PRESSURE PID 
    • Firmly press and release the brake pedal while monitoring the ABS module MC_PRESS PID.
    • Does the PID increase with increased brake pedal pressure and decrease with decreased brake pedal pressure? 
    1. 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.
    2. NO  : INSTALL a new HCU. REFER to Hydraulic Control Unit (HCU) . CALIBRATE the ABS module. FOLLOW the scan tool directions for the calibration procedure. CLEAR the DTCs. CARRY OUT the self-test with the brake pedal not applied.
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