Pinpoint Test M: DTCs C0021:21, 66 and 77
Anti-Lock Control - Hybrid
Pinpoint Tests
Pinpoint Test M: DTCs C0021:21, 66 and 77
Normal Operation
The ABS module will measure the amount of hydraulic brake pressure generated every time the brakes are applied. The ABS module will also test 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 will utilize 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 regenerative brake system will transition from brake-by-wire mode into low temperature conventional mode. While in low temperature conventional mode, the ABS module will continue to test the brake booster. If the brake booster begins to generate the expected amount of pressure in hydraulic system, the regenerative brake system will recover into brake-by-wire mode. If the regenerative 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 regenerative brake system will downgrade to conventional brake pedal operation for the rest of the ignition cycle.
- DTC C0021:21 (Brake Booster Performance: Signal Amplitude < Minimum) - If the brake booster is not able to build adequate hydraulic brake pressure when the brakes are applied either though input from the driver or when the ABS module checks the brake booster, this DTC will set. In most cases this DTC will set if the vehicle was started at low ambient temperatures, otherwise this DTC will set as a result of other brake booster DTCs or other DTCs that indicate a fault with ABS module inputs from the, brake pedal angle sensor, hydraulic brake pressure sensors or vacuum pressure sensor. 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. This DTC is for information only. This DTC will 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.
- 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 will downgrade to conventional mode until the cause of DTC C0021:21 has been corrected. The red brake warning indicator will illuminate when this DTC is set.
- 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 will set. This DTC will 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:
- ABS module
- Brake booster
- Brake master cylinder
- HCU
- Air in the hydraulic brake system
- Vacuum hoses, lines and fittings
PINPOINT TEST M: DTCs C0021:21, 66 AND 77
NOTICE: Use the Flex Probe Kit for all test connections to prevent damage to the wiring terminals. Do not use standard multi-meter probes.
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M1 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
GO to M2.
No
The other ABS module DTCs will indicate the cause of DTCs C0021:21, 66 and/or 77.
CORRECT all other ABS module DTCs. REFER to the ABS Module DTC Chart. Diagnostic Trouble Code Tests and Associated Procedures
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M2 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 M3.
No
REPAIR or INSTALL new components as necessary. REFER to Hydraulic System, Brakes &/or Brake Pedal Assy.
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M3 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 M4.
No
REPAIR or INSTALL new components as necessary. REFER to Power Brake Assist for the brake booster. REFER to Hydraulic System, Brakes &/or Brake Pedal Assy for the brake master cylinder.
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M4 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 M5.
No
REPAIR or INSTALL new components as necessary. REFER to Power Brake Assist.
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M5 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. CARRY OUT the brake system service bleed. REFER to Brake System Bleeding - Hybrid in Brakes and Traction Control.
No
GO to M6.
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M6 CHECK FOR AIR IN THE BRAKE SYSTEM
- Carry out the brake system service bleed. Refer to Brake System Bleeding in Brakes and Traction Control.
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: Self Test - Clear all 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 M7.
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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M7 CHECK FOR CORRECT ABS MODULE OPERATION
- Disconnect: ABS Module C155 .
- Check for:
- corrosion.
- pushed-out pins.
- spread terminals.
- Connect: ABS Module C155 .
- Make sure the connector is seated 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 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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