U121C Diagnostic Trouble Code

U121C is a kind of OBD-II Diagnostic U-Network 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 U121C diagnostic trouble code may include:

The engine oil will exhibit dilution from the ECUs attempts to increase engine temperature. Some vehicles advance the fuel injection timing slightly after top center to afterburn a small amount of fuel to increase exhaust temperatures. Some of this fuel enters the crankcase. When the ECU determines the necessity to regenerate the DPF, the service life of the oil be shortened significantly
Faulty or damaged wiring
Hesitation upon acceleration
Rich or lean exhaust

Possible Causes :

Faulty IMRC actuator relay (if equipped)
A large air leak at or near the number one oxygen sensor would also cause a lean mixture.
Defective ECU strategies or components will prevent proper regeneration

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. Look at the plug wires to make sure they are not burnt or laying on the exhaust.

Process Tips

Diagnostic trouble code U121C 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 U121C.

Fortunately, U121C is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

U121C Trouble Code For Specific Cars

U121C Datsun Sports HO2S Heater Control Circuit High (Bank 1 Sensor 2)
U121C Toyota Tazz Passenger Mirror Horizontal / Vertical Feedback Potentiometer Circuit Open
U121C Mercedes-benz Slr Class Air Suspension Front Inflator Solenoid Output Circuit Short To Ground
U121C Austin 8 Autolamp Delay Circuit Short To Ground
U121C Vauxhall Victor Pressure Control Solenoid Malfunction
U121C Nissan Laurel Column Reach Feedback Potentiometer Circuit Open
U121C Mini Clubman APLSOL Solenoid Circuit Malfunction