Pinpoint Test L : C0021:00, C0021:21, C0021:66, C0021:77: Notes
Refer to Vehicle Dynamic Systems for schematic and connector information.
Normal Operation and Fault Conditions
The ABS module measures the amount of hydraulic brake pressure generated every time the friction 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 uses input from the brake pedal travel sensor, brake booster diaphragm travel sensor, the brake pressure sensors internal to the HCU and the vacuum pressure sensor to determine if the required amount of hydraulic brake pressure is being generated. If the ABS module determines the brake booster is not able to generate adequate hydraulic brake pressure in the master cylinder, the brake system transitions from regenerative braking mode into friction braking mode. While in friction braking mode, the ABS module continues to test the brake booster. If the brake booster begins to generate the expected amount of pressure in the hydraulic system, the brake system recovers into regenerative braking mode. If the brake system has to transition from regenerative braking mode to friction braking mode 3 times in the same ignition cycle because of a brake booster performance fault, the brake system downgrades to friction braking for the rest of the ignition cycle.
The SOBDMC monitors fault messages from the ABS module. When the ABS module sets DTC C0021:21, C0021:66, C0021:77 or C1015:64, the SOBDMC sets a DTC and illuminates the MIL.
DTC Fault Trigger Conditions
| DTC | Description | Fault Trigger Conditions |
|---|---|---|
| C0021:00 | Brake Booster Performance: No Sub Type Information | The SOBDMC sets this DTC when the ABS module sets DTC C0021:21, C0021:66, C0021:77 or C1015:64. |
| C0021:21 | Brake Booster Performance: Signal Amplitude < Minimum | This DTC sets if the brake booster is not able to generate adequate hydraulic brake pressure when the brakes are applied either through input from the driver or when the ABS module checks the brake booster. 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 also sets as a result of other brake booster, brake pedal travel sensor, hydraulic brake pressure sensors or vacuum pressure sensor Diagnostic Trouble Codes (DTCs) being set. |
| C0021:66 | Brake Booster Performance: Signal Has Too Many Transitions / Events | This DTC indicates the regenerative brake system has switched from regenerative braking mode to friction braking mode 3 times due to the cause of DTC C0021:21. When this DTC is present, the brake system reverts to friction braking mode until the cause of DTC C0021:21 has been corrected. The red brake warning indicator illuminates when this DTC is set. If Diagnostic Trouble Codes (DTCs) C0021:21 and 66 are the only brake booster performance codes 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. |
| C0021:77 | Brake Booster Performance: Commanded Position Not Reachable | This DTC is for information only and does not indicate a fault with the brake system. This DTC sets if the hydraulic brake pressure does not change when the ABS module checks the brake booster. 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 Diagnostic Trouble Codes (DTCs) retrieved along with this DTC. |
Possible Causes
- Wiring, terminals or connectors
- Vacuum leaks
- Brake fluid leaks
- Air in the brake hydraulic system
- Brake pedal and bracket
- Brake booster
- Master cylinder
- ABS module