C121E Diagnostic Trouble Code

C121E 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 C121E diagnostic trouble code may include:

Rich or lean exhaust
Fuel pressure too low
Engine surge
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)
Faulty IMRC actuator/sensor

Repair Processes :

You might continue by connecting the scanner to the vehicle diagnostic connector and retrieving all stored codes and freeze frame data. 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. 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 C121E 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 C121E.

Fortunately, C121E is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

C121E Trouble Code For Specific Cars

C121E Renault Kadjar Glow Plug/Heater Circuit "B" Malfunction
C121E Amc Concorde Air Suspension Front Height Sensor High (SE) Signal Circuit Short To Battery
C121E Simca Vedette Beaulieu Intermediate Speed Sensor (ISS) Malfunction
C121E Bianchi S Brake Pedal Input Circuit Ground Short
C121E Audi Q7 ASM Control Circuit High
C121E Vauxhall Sintra Pressure Control Solenoid C Control Circuit Low
C121E Mg Ya Ambient Air Temperature Sensor Circuit Intermittent