C21AC Diagnostic Trouble Code

C21AC 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 C21AC diagnostic trouble code may include:

Faulty O2 Sensor
Lack of power
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 :

A large air leak at or near the number one oxygen sensor would also cause a lean mixture.
Faulty IMRC actuator relay (if equipped)
Fuel with a large percentage of sulfur will clog the DPF quickly

Repair Processes :

You might continue by connecting the scanner to the vehicle diagnostic connector and retrieving all stored codes and freeze frame data. 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. 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.

Process Tips

Diagnostic trouble code C21AC 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 C21AC.

Fortunately, C21AC is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

C21AC Trouble Code For Specific Cars

C21AC Turner Gt Pedal Position Sensor Disagreement btwn Sensors
C21AC Renault Laguna Ground ECU Circuit Open
C21AC Oldsmobile Alero Cylinder 6 Injector Circuit Low
C21AC Pontiac G6 Exhaust Valve Control Solenoid Circuit (Bank 1)
C21AC Honda Acura Mdx Pressure Control Solenoid B Electrical
C21AC Austin 12 Audio Reverse Aid Mute Input Ckt Failure
C21AC Mercury Mountaineer Air Suspension Rear Height Sensor Low Signal Circuit Short To Ground