PINPOINT TEST Q: DTCs C0021:21, 66 AND 77

WARNING: This page is about a different car, the 2010 Mercury Milan, 2010 Lincoln MKZ, and 2010 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Use the Flex Probe Kit for all test connections to prevent damage to the wiring terminals. Do not use standard multimeter probes.

Q1 CHECK THE DTCs FROM THE SELF-TEST
- Review the DTCs retrieved and recorded in INSPECTION AND VERIFICATION .
- Are other DTCs present along with DTC C0021:21, 66 or 77?
- Yes: The other ABS module DTCs will indicate the cause of DTCs C0021:21, 66 and/or 77.
  DIAGNOSE all other ABS module DTCs before diagnosing DTC C0021:21, 66 or 77. REFER to ABS MODULE DTC TABLE .
- No: GO to Q2.
Q2 CHECK THE BRAKE PEDAL AND BRACKET
- Inspect the brake pedal and bracket and the clevis end of the booster push rod for misalignment or damage. Verify that all brake pedal and bracket fasteners are tightened to the specified torque. Apply and release the brake pedal. Verify that the brake pedal moves freely and returns to the full released position.
- Is the brake pedal and bracket OK?
- Yes: GO to Q3.
- No: REPAIR or INSTALL new components as necessary. REFER to HYDRAULIC BRAKE ACTUATION .
Q3 CHECK THE BRAKE BOOSTER AND BRAKE MASTER CYLINDER
- Inspect the brake booster and brake master cylinder for misalignment or damage. Verify that all brake booster and master cylinder fasteners are tightened to the specified torque.
- Is the brake booster and the brake master cylinder OK?
- Yes: GO to Q4.
- No: REPAIR or INSTALL new components as necessary. REFER to REMOVAL AND INSTALLATION for the brake booster. REFER to REMOVAL AND INSTALLATION for the brake master cylinder.
Q4 CHECK FOR VACUUM LEAKS
- Inspect the vacuum pump and brake booster vacuum hoses, lines and fittings for vacuum leaks.
- Are the vacuum pump and brake booster vacuum hoses, lines and fittings OK?
- Yes: GO to Q5.
- No: REPAIR or INSTALL new components as necessary. REFER to POWER BRAKE ACTUATION .
Q5 CHECK THE BRAKE SYSTEM FOR BRAKE FLUID LEAKS
- Inspect the brake system for brake fluid leaks.
- Are any brake fluid leaks found?
- Yes: REPAIR as necessary. FILL the brake master cylinder reservoir using the specified brake fluid. BLEED the brake system, REFER to BRAKE SYSTEM BLEEDING .
- No: GO to Q6.
Q6 CHECK FOR AIR IN THE BRAKE SYSTEM
- Bleed the brake system, refer to BRAKE SYSTEM BLEEDING .
- Ignition ON.
- Using the scan tool, clear all Continuous Memory Diagnostic Trouble Codes (CMDTCs).
- Disconnect the scan tool.
- Test drive the vehicle at speeds greater than 32 km/h (20 mph).
- Connect the scan tool.
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: Self Test - ABS Module.
- Carry out the ABS module self-test.
- Are DTCs C0021:21, 66 and 77 present?
- Yes: GO to Q7.
- No: The system is operating correctly at this time. The concern may have been caused by air trapped in the hydraulic brake system. CLEAR the DTCs. REPEAT the self-test.
Q7 CHECK FOR CORRECT ABS MODULE OPERATION
- Disconnect: ABS Module C135.
- Using a good light source, carefully inspect ABS module connector C135 for corroded terminals.
- Inspect for any pushed-out pins.
  Refer to the appropriate SYSTEM WIRING DIAGRAMS article for schematic and connector information.
- Using a suitable mating terminal, check each female terminal for deformed or enlarged contacts by comparing the mating terminal's fit between each pin location.
  Refer to the appropriate SYSTEM WIRING DIAGRAMS article for schematic and connector information.
- Connect: ABS Module C135.
- Make sure the connector seats correctly, then operate the system and verify the concern is still present.
- Is the concern still present?
- Yes: INSTALL a ABS module. REFER to Removal and Installation . TEST the system for normal operation. CLEAR the DTCs. DRIVE the vehicle.
  REPEAT the self-test. If the DTCs identified in the normal operation of this pinpoint test are retrieved, INSTALL a new HCU. REFER to Removal and Installation .
- No: 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.