P1221 Diagnostic Trouble Code

P1221 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 P1221 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 :

Check to make sure they are not burnt or corroded. If in doubt, get some Electrical Contact cleaner at any parts store if cleaning of the terminals is needed. 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. 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.

Process Tips

Diagnostic trouble code P1221 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 P1221.

Fortunately, P1221 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

P1221 Trouble Code For Specific Cars

P1221 Isuzu Bellett
P1221 Mitsubishi Space Liner Aux Heater Overheat Sensor Circuit Open
P1221 Triumph 1300 Passenger Window Up / Down Power Circuit Short to Ground
P1221 Infiniti I30
P1221 Chevrolet Nova EGR Drive Overcurrent
P1221 Suzuki X-90 Mirror Driver Vertical Switch Circuit Failure
P1221 Subaru Forester 3 Left Lamp Outage Signal Circuit Short to Ground