C0021 Code: Meaning, Causes, and Symptoms | OBD2 Codes
C0021 – Brake Booster Performance
C0021 Possible Symptoms
Anti-Lock Brake System (ABS) Warning Light ON,Engine Light ON (or Service Engine Soon Warning Light)
C0021 Possible Causes
Faulty Brake Booster,Faulty Vacuum Pressure Sensor,Vacuum Pressure Sensor harness is open or shorted,Vacuum Pressure Sensor circuit poor electrical connection
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 -200 mbar (-2.90 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.