C0021

C0021 - Brake Booster Performance






For a complete wiring diagram, refer to.

• 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 ignition-ON) and if the engine is running more than 600 RPM there should be at least -135 mbar (-1.958 psi) of differential pressure in the vacuum-chamber for boosting the pedal force. If the pressure remains less than this value for more than A) 1 sec., if brake is applied, B) 2 min., if brake is not applied, but throttle position is less than 30%, C) 10 min., if brake is not applied and throttle position is over 30%, and vehicle speed is over 1 m.p.h. (2 km/h), a booster vacuum failure is reported.






Test Step 1 - Test for A DTC C0021 Brake Booster Performance

• This DTC must be active for the results of this test to be valid.

• Turn the ignition ON.

• With the scan tool, read and record the DTCs.

• With the scan tool, read and record Environmental Data to help identify the conditions in which the DTC was set.

• With the scan tool, erase the DTCs.

• Start the engine.

• Depress and release the brake pedal.

• With the scan tool, read and record the DTCs.

Does the scan tool display C0021 - Brake Booster Performance?

Yes

• Go to Test Step 2 => [ Test Step 2 - Test for Pinched Vacuum Supply Line ]

No

• Perform the ABS Intermittent Condition Test. Refer to => Non-DTC Based Diagnostics. ABS Intermittent Condition Test

Test Step 2 - Test for Pinched Vacuum Supply Line

• Turn the ignition OFF.

• Test the vacuum supply line to brake booster for a pinched, cut or open hose.

Were any problems found?

Yes

• Repair as necessary.

• Perform ABS Verification Test. Refer to => Non-DTC
Based Diagnostics. ABS Verification Test

No

• Go to Test Step 3 => [ Test Step 3 - Test for Vacuum Pressure Signal Change ]

Test Step 3 - Test for Vacuum Pressure Signal Change

• Turn the ignition ON.

• Remove the vacuum pressure sensor from the booster.

• Connect a vacuum pump to the vacuum pressure sensor.

• Apply vacuum to the vacuum pressure sensor and watch for signal change.

Is the voltage signal changing on the scan tool as vacuum is being applied?

Yes

• Go to Test Step 4 => [ Test Step 4 - Test Brake Booster Test Valve ]

No

• Replace the vacuum pressure sensor.

• Perform ABS Verification Test. Refer to => Non-DTC
Based Diagnostics. ABS Verification Test

Test Step 4 - Test Brake Booster Test Valve

• Remove the brake booster test valve.

• Apply vacuum to the booster side of the test valve.

Is the brake booster test valve holding vacuum?

Yes

• Replace the brake booster.

• Perform ABS Verification Test. Refer to => Non-DTC
Based Diagnostics. ABS Verification Test

No

• Replace brake booster test valve.

• Perform ABS Verification Test. Refer to => Non-DTC
Based Diagnostics. ABS Verification Test