P0021 Diagnostic Trouble Code

P0021 is a kind of OBD-II Diagnostic P-Powertrain 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 P0021 diagnostic trouble code may include:

Cherry red hot catalytic converter
Poor acceleration
The light may stay on or light intermittently as the DPF regenerates. The engine will be sluggish on acceleration.
If the DPF is not cleared the ECU will revert to the "Limp Home Mode" until the situation is corrected

Possible Causes :

A large air leak at or near the number one oxygen sensor would also cause a lean mixture.
Faulty IMRC actuator relay (if equipped)
An air leak forward of the DPF will change the sensor readings resulting in the code

Repair Processes :

If the scan tool has that capability, and the scan tool can operate the IMRC valves, then the problem is either resolved and a simple code clearing is all that's left or a new PCM would be called for. Look for missing ground strap or a rusty ground where the fuel tank is grounded to the frame. Check for damage to the wiring harness connector.

Process Tips

Diagnostic trouble code P0021 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 P0021.

Fortunately, P0021 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

P0021 Trouble Code For Specific Cars

P0021 Bugatti Eb112 Cylinder #4 High To Low Side Short
P0021 Ferrari 612 Intake Valve Control Solenoid Circuit High (Bank 2)
P0021 Mitsubishi Cz Audio Steering Wheel Control Unit is Not Responding
P0021 Buick 50 Cylinder 3 Misfire Detected
P0021 Humber Imperial Right Rear Sensor Circuit Failure
P0021 Alfa 24 ABS Outlet Valve Coil Rear Circuit Short To Ground
P0021 Alfa Romeo 4c Accelerometer Front Circuit Failure