P121D Diagnostic Trouble Code

P121D 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 P121D diagnostic trouble code may include:

Fuel pressure too high
Diminished fuel efficiency
Rich or lean exhaust
Lack of power

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 relay (if equipped)

Repair Processes :

Find out what kind of system you have and verify that voltage to the fuel level sensor is present at the fuel pump wiring harness. Look at the plug wires to make sure they are not burnt or laying on the exhaust. If you find a related TSB, the information will often help in diagnosing the code in question as TSBs are crested from many thousands of repairs.

Process Tips

Diagnostic trouble code P121D 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 P121D.

Fortunately, P121D is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

P121D Trouble Code For Specific Cars

P121D Avanti Avanti Aux Heater Glow Plug Circuit Short to Ground
P121D Rovin Motocar Ignition Key-In Circuit Short To Battery
P121D Talbot 110 Mirror Passenger Down Circuit Open
P121D Chevrolet Niva EGR Calibration High
P121D Mg Xpower Ambient Air Temperature Sensor Circuit High
P121D Ferrari 340 Intake Air Temperature (IAT) Sensor Circuit Intermittent High Voltage
P121D Nissan 180 Child Seat Detection Circuit Short to Ground