Pinpoint Test Q: DTCs C0021:21, 66 and 77
Anti-Lock Control - Hybrid
Pinpoint Test Q: DTCs C0021:21, 66 and 77
Normal Operation
The ABS module measures the amount of hydraulic brake pressure generated every time the brakes are applied. The ABS module tests the brake booster every key cycle by operating the brake booster independently of brake pedal input and measuring the hydraulic brake pressure generated. The ABS module utilizes input from the brake pedal angle sensor, brake booster travel sensor, the brake pressure sensors internal to the Hydraulic Control Unit (HCU) and the vacuum pressure sensor to determine if the required amount of hydraulic brake pressure is being generated. If the ABS module detects that the brake booster is not able to build adequate hydraulic brake pressure in the master cylinder, the brake system transitions from brake-by-wire mode into low temperature conventional mode. While in low temperature conventional mode, the ABS module continues to test the brake booster. If the brake booster begins to generate the expected amount of pressure in hydraulic system, the brake system recovers into brake-by-wire mode. If the brake system has to transition from brake-by-wire mode to low temperature conventional mode 3 times in the same ignition cycle because of a brake booster performance fault, the brake system downgrades to conventional brake pedal operation for the rest of the ignition cycle.
- DTC C0021:21 (Brake Booster Performance: Signal Amplitude < Minimum) - This DTC is for information only and does not cause any indicators to illuminate. However, other DTCs that cause DTC C0021:21 to set may cause indicators to illuminate. If the red brake warning indicator is illuminated, diagnose all other DTCs before diagnosing DTC C0021:21. Otherwise, disregard DTC C0021:21.
- If the brake booster is not able to build adequate hydraulic brake pressure when the brakes are applied either through input from the driver or when the ABS module checks the brake booster, DTC C0021:21 sets. In most cases DTC C0021:21 sets if the vehicle was started in low ambient temperatures or as a result of low ambient temperatures causing slow booster reaction time. This DTC set as a result of other brake booster, brake pedal angle sensor, hydraulic brake pressure sensors or vacuum pressure sensor DTCs being set.
- DTC C0021:66 (Brake Booster Performance: Signal Has Too Many Transitions) - This DTC indicates that the regenerative brake system has switched from brake-by-wire mode to low temperature conventional mode 3 times due to the cause of DTC C0021:21. When this DTC is present, the regenerative brake system downgrades to conventional mode until the cause of DTC C0021:21 has been corrected. The red brake warning indicator illuminates when this DTC is set. If only DTCs C0021:21 and 66 are present, there is likely to be mechanical damage to the brake booster, brake pedal and bracket, master cylinder, a hydraulic brake fluid leak, air trapped in the hydraulic system or a vacuum leak may be present.
- DTC C0021:77 (Brake Booster Performance: Commanded Position is Not Reachable) - This DTC is for information only and does not indicate a fault with the brake system. If the hydraulic brake pressure does not change when the ABS module checks the brake booster, this DTC sets. This DTC does not cause any indicators to illuminate and may set as a result of low ambient temperatures causing slow booster reaction time. If the red brake warning indicator is not illuminated, this DTC should be disregarded. Diagnose all other DTCs retrieved along with this DTC.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- Wheel speed sensor
- ABS module
PINPOINT TEST Q: DTCs C0021:21, 66 AND 77
NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
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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 Chart. ABS Module DTC Chart
No
GO to Q2.
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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.
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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 Service and Repair for the brake booster. REFER to Hydraulic Brake Actuation Brake Master Cylinder for the brake master cylinder.
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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.
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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 Brake System Bleeding.
No
GO to Q6.
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Q6 CHECK FOR AIR IN THE BRAKE SYSTEM
- Bleed the brake system, refer to Brake System Bleeding in Brake System - General Information 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.
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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 Wiring Diagram Set 5 (Fusion/Milan/MKZ, Fusion Hybrid, Milan Hybrid, MKZ Hybrid) for schematic and connector information. Diagrams By Number
- 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 Wiring Diagram Set 5 (Fusion/Milan/MKZ, Fusion Hybrid, Milan Hybrid, MKZ Hybrid) for schematic and connector information. Diagrams By Number
- 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 Service and Repair. 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 Service and Repair.
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.
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