P121B Diagnostic Trouble Code

P121B is a kind of OBD-II Diagnostic P-Powertrain 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 P121B diagnostic trouble code may include:

Diminished fuel efficiency
Fuel pressure too high
Malfunction Indicator Lamp (MIL) illuminated
The light may stay on or light intermittently as the DPF regenerates. The engine will be sluggish on acceleration.

Possible Causes :

Low fuel pressure caused by a clogged filter, failing fuel pump, failed fuel pressure regulator or clogged or leaking injectors.
Low fuel pressure caused by a clogged filter, failing fuel pump, failed fuel pressure regulator or clogged or leaking injectors.
Faulty IMRC actuator/sensor

Repair Processes :

Look for damage to the tank indicating impact that may have damaged the fuel pump or sender. If the scan tool has that capability, and the scan tool can operate the IMRC valves, then the problem is either resolved and a simple code clearing is all that's left or a new PCM would be called for.

Process Tips

Diagnostic trouble code P121B 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 P121B.

Fortunately, P121B is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

P121B Trouble Code For Specific Cars

P121B Rover 10 Idle Control System Circuit Shorted
P121B Acura El ABS Hydraulic Pressure Differential Switch Input Short Circuit To Ground
P121B Fiat Ritmo Lateral Accelerometer circuit Failure
P121B Lada 1200 SGC (Cam Position) Sensor Circuit Malfunction/ Crankshaft Position - Camshaft Position Correlation
P121B Ford E-series Memory #1 output Short to Ground
P121B Irmscher Gt
P121B Lamborghini P Solenoid Current Out Of Range