U121F Diagnostic Trouble Code

U121F 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 U121F diagnostic trouble code may include:

Diminished fuel efficiency
Fuel pressure too high
Malfunction Indicator Lamp (MIL) illuminated
Rich or lean exhaust

Possible Causes :

The Mass Airflow sensor will also cause this problem. Mass Airflow circuit malfunction.
Fuel with a large percentage of sulfur will clog the DPF quickly
Faulty IMRC actuator/sensor

Repair Processes :

Look for damage to the tank indicating impact that may have damaged the fuel pump or sender. Use the DVOM to test resistance and continuity on all system circuits if actuator and sensor resistance levels are in compliance with manufacturer's specifications.

Process Tips

Diagnostic trouble code U121F 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 U121F.

Fortunately, U121F is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

U121F Trouble Code For Specific Cars

U121F Aston Martin Am Vantage Air Suspension RF Height Sensor Circuit Short To Battery
U121F Citroen Ln
U121F Pininfarina Rosso Evap Emission Control Sys Vent Control Valve Circuit
U121F Smart Roadster Lamp Anti-Theft Indicator Circuit Short To Battery
U121F Nissan El Grand Clutch Pedal Switch B Circuit
U121F Mg Ex-e Air Suspension RR Air Spring/Shock Solenoid Output Circuit Short To Battery
U121F Suzuki Light Mirror Driver Horizontal Feedback Potentiometer Circuit Open