C0021

C0021-02-BRAKE BOOSTER - GENERAL SIGNAL FAILURE

For a complete wiring diagram, refer to the Wiring Information.

- When Monitored:
With the ignition on.

- Set Condition:
When the Vacuum Pressure Sensor indicates a failure in the Vacuum Booster. After the cold start phase (i.e. 3 min after engine is running) and if the engine is running above 600 RPM there should be at least -135 mbar (-1.96 psi) of differential pressure in the vacuum-chamber for boosting the pedal force. If the pressure remains below this value for more than two minutes. Timer resets if the pressure remains above 220 mbar (3.19 psi) for 10 seconds.





NOTE: If DTC C1252-92 is present, perform the diagnostics for this DTC before continuing with this diagnostic procedure.

1. VERIFY THE DTC IS ACTIVE
1. Turn the ignition on.
2. With the scan tool, read and record the DTCs.
3. With the scan tool, read and record Environmental Data to help identify the conditions in which the DTC was set.
4. With the scan tool, erase the DTCs.
5. Start the engine.
6. Press and release the brake pedal.
7. Wait five minutes or until red brake lamp illuminates.

WARNING: To avoid possible serious or fatal injury, check brake capability is available before road testing.

8. Test drive the vehicle at speeds above 10 km/h (6 mph).
9. With the scan tool, read and record the DTCs.

Is the DTC Active at this time?

Yes

- Go To 2

No

- Check the vacuum supply line to brake booster for a pinched, cut, loose or cracked vacuum hose which could cause an intermittent condition.
- Perform the ABS-INTERMITTENT CONDITION TEST. Testing and Inspection.

2. CHECK VACUUM SUPPLY LINE
1. Turn the ignition off.
2. Check the vacuum supply line to brake booster for a pinched, cut, loose or open vacuum hose.
3. Disconnect the booster vacuum supply line and attach a vacuum pressure gauge.
4. Start the engine.

Does the vacuum fluctuate with RPM change?

Yes

- Repair as necessary.
- Perform the ABS VERIFICATION TEST. ABS Verification Test.

No

- Go To 3

3. CHECK FOR VACUUM PRESSURE SIGNAL CHANGE
1. Turn the ignition on.
2. Remove the Vacuum Pressure Sensor from the Booster.
3. Block off the vacuum feed port.
4. Connect a vacuum pump to the Vacuum Pressure Sensor.
5. Apply vacuum to the Vacuum Pressure Sensor.
6. Using the scan tool, and a pressure gauge watch for the signal change.
7. Using the scan tool, watch for signal change.

Is the signal changing and does it compare to the pressure gauge reading?

Yes

- Go To 4

No

- Replace the Vacuum Pressure Sensor. Power Brake Booster - Removal.
- Perform the ABS VERIFICATION TEST. ABS Verification Test.

4. CHECK BRAKE BOOSTER CHECK VALVE
1. Remove the Brake Booster Check Valve.
2. Apply vacuum to the booster side of the check valve.

Is the Brake Booster Check Valve holding vacuum?

Yes

- Replace the Brake Booster. Power Brake Booster - Removal.
- Perform the ABS VERIFICATION TEST. ABS Verification Test.

No

- Replace Brake Booster Check Valve. Power Brake Booster - Removal.
- Perform the ABS VERIFICATION TEST. ABS Verification Test.