C0021 Diagnostic Trouble Code

C0021 is a kind of OBD-II Diagnostic C-Chassis Diagnostic Trouble Code.

It is considered generic because it applies to all makes and models of vehicles, although specific repair steps may be different depending on your car model.

Symptoms

Symptoms of a C0021 diagnostic trouble code may include:

Reduction in engine performance, especially at low RPM levels
Vacuum leak on the engine
Diminished fuel efficiency
Engine surge

Possible Causes :

Rusty exhaust systems, cracked exhaust manifolds or damaged or missing gaskets or donuts will cause air leaks.
An air leak forward of the DPF will change the sensor readings resulting in the code
Dirty air cleaner element Damaged DPF

Repair Processes :

Oxygen sensors signal the engine management computer the amount of oxygen present in the exhaust, which is used in determining and controlling the fuel ratio. It should be pretty close to battery voltage (12 volts). If not, then this is the circuit that has the problem. Find out what kind of system you have and verify that voltage to the fuel level sensor is present at the fuel pump wiring harness.

Process Tips

Diagnostic trouble code C0021 is not difficult to diagnose and repair. Thus, it always pays to have a qualified technician to look after your vehicle should this error code arise.

Diagnosing this code requires the engine to be in good running shape, without unmetered air entering the engine. If other codes that relates to misfiring condition, lean running or air entering the engine is present, then you must first fix those error codes before C0021.

Fortunately, C0021 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

C0021 Trouble Code For Specific Cars

C0021 Aston Martin 15 Air Suspension RF Corner Up Timeout
C0021 Chevrolet Monza EGR Calibration Fault
C0021 Renault Dauphine Gear Shift Position Circuit Low
C0021 Bertone Blitz Brake Motor Warning lamp Circuit Short to Vbatt
C0021 Peugeot 406 EIC Switch-1 Assembly Circuit Failure
C0021 Alfa Romeo 1900 ABS Power Relay Output Short Circuit To Battery
C0021 Mazda Washu A/C Post Heater Sensor #2 Circuit Failure