C121A Diagnostic Trouble Code

C121A 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 C121A 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 :

Fuel with a large percentage of sulfur will clog the DPF quickly
The Mass Airflow sensor will also cause this problem. Mass Airflow circuit malfunction.
An air leak forward of the DPF will change the sensor readings resulting in the code

Repair Processes :

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. Once located, visually inspect the connectors and wiring. Look for rubbing, scraping, bare wires, worn spots or melted plastic connectors.

Process Tips

Diagnostic trouble code C121A 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 C121A.

Fortunately, C121A is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

C121A Trouble Code For Specific Cars

C121A Daimler 4.5-litre Hazard Flash Output Circuit Short To Ground
C121A Pontiac Aztec Exhaust Pressure Control Valve Intermittent
C121A Chevrolet Matiz EGI Glow Plug Primary Failure
C121A Holden Tx Power Window One Touch Up/Down Activated Simultaneously
C121A Renault Rs Heater Coolant Temp sensor circuit Short to GND
C121A Oldsmobile 76 Cylinder 5 Injector Circuit High
C121A Citroen Gsa Fuel Pressure Regulator 1 Control Circuit