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

WARNING: This page is about a different car, the 2011 Mercury Milan, 2011 Lincoln MKZ, and 2011 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.

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

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 indicates 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 the ABS MODULE DTC TABLE in this service information.
- 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 SYSTEM ACTUATION article.
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 POWER BRAKE ACTUATION -- BRAKE BOOSTER article for the brake booster. REFER to HYDRAULIC BRAKE SYSTEM ACTUATION article 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 -- BRAKE BOOSTER article.
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 in BRAKE SYSTEM - GENERAL INFORMATION article.
- No : GO to Q6.
Q6 CHECK FOR AIR IN THE BRAKE SYSTEM
- Bleed the brake system, refer to Brake System Bleeding in BRAKE SYSTEM - GENERAL INFORMATION article.
- 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 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 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 ANTI-LOCK BRAKE SYSTEM (ABS) MODULE - HYBRID in this service information. 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 HYDRAULIC CONTROL UNIT (HCU) - HYBRID in this service information.
- 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.