P009B: Fuel Pressure Relief Control Circuit/Open

What does P009B mean?

The fuel pressure relief control is an electrically controlled valve on the fuel rail that the engine control module opens to reduce rail pressure deliberately, for example on overrun, on load drops or when the engine is switched off. It differs from the purely mechanical pressure relief valve, which opens passively at overpressure, and from the pressure regulator, which controls pressure continuously. Manufacturer documents show this code mainly on heavy-duty diesel engines. P009B reports an open control circuit of this valve. Rail pressure can then not be reduced as intended, and the engine may be derated.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Check engine light on
• Reduced power (derate) possible

Common causes

• High Wire broken or connector corroded
• Medium Valve coil faulty
• Low Output driver in the engine control module faulty

Likelihood is a general estimate across vehicles; your make and model may differ.