B0121 Diagnostic Trouble Code

B0121 is a kind of OBD-II Diagnostic B-Body 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 B0121 diagnostic trouble code may include:

Faulty O2 Sensor
Lack of power
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 :

A large air leak at or near the number one oxygen sensor would also cause a lean mixture.
Faulty IMRC actuator relay (if equipped)
Fuel with a large percentage of sulfur will clog the DPF quickly

Repair Processes :

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. 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.

Process Tips

Diagnostic trouble code B0121 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 B0121.

Fortunately, B0121 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

B0121 Trouble Code For Specific Cars

B0121 Toyota Progres Park Brake Applied Warning Lamp Circuit Failure
B0121 Nissan Pixo Cooling Fan Power/Ground Circuit Malfunction
B0121 Volvo 360
B0121 Sunbeam 3-litre Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent
B0121 Bristol 409 Crankshaft Position Camshaft Position Correlation (Bank 1 Sensor A)
B0121 Cunningham Roadster Fuel Temperature Sensor #1 Circuit Short to Ground
B0121 Bentley Azure Battery Power Supply ECU Circuit Failure