C0721 Diagnostic Trouble Code

C0721 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 C0721 diagnostic trouble code may include:

The light may stay on or light intermittently as the DPF regenerates. The engine will be sluggish on acceleration.
Faulty PCM
If the DPF is not cleared the ECU will revert to the "Limp Home Mode" until the situation is corrected
Diminished fuel efficiency

Possible Causes :

The Mass Airflow sensor is a hot wire that senses the volume of air entering the intake manifold. The computer uses this information to control fuel mixture.
Defective ECU strategies or components will prevent proper regeneration
An air leak forward of the DPF will change the sensor readings resulting in the code

Repair Processes :

Replace the oxygen sensor that is downstream from the catalytic converter on the side of the engine that does not contain cylinder #1. Also, if a oxygen sensor code stating "heater circuit malfunction" the sensor has most probably failed. With the valve disconnected, the red voltmeter lead should be attached to the IMRC valve power wire and the black voltmeter lead connected to ground. It should be pretty close to battery voltage (12 volts). If not, then this is the circuit that has the problem.

Process Tips

Diagnostic trouble code C0721 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 C0721.

Fortunately, C0721 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

C0721 Trouble Code For Specific Cars

C0721 Paykan Saloon Driver's / Passenger's Door Ajar Output Circuit Failure
C0721 Rumpler Tropfenwagen Ignition Run Circuit Failure
C0721 Frazer Six NVM RF HR Failure
C0721 Ford F-450 Metering Oil Pump Position Sensor Circuit Malfunction
C0721 Zundapp Janus Seat Belt Switch Circuit Short To Ground
C0721 Jaguar E-type Seat Driver Forward Switch Circuit Failure
C0721 Eagle Summit Incorrect Gear Ratio