What does it mean?
On modern direct-injection gasoline engines and diesel engines, the high-pressure fuel pump is mounted on the engine. This mechanical pump is capable of upwards of 10,000 psi. Fuel pressure regulation is different than in low-pressure fuel injection systems, controlled electronically instead of mechanically. As the mechanical fuel pump is mounted on the cam shaft, it is constantly pumping. Depending on system design, there are a few ways to modulate fuel rail pressure.
On some return-less systems, fuel pressure is modulated by a variable-speed low-pressure supply pump controlled by the engine control module (ECM). Other return-less and fuel-return systems regulate fuel pressure using an ECM-controlled fuel pressure regulator (FPR). Some of these regulate how much fuel enters the pump itself, while others regulate how much fuel bleeds back to the tank, via the fuel-return line. The FPR may be mounted on the high-pressure fuel pump or on the fuel rail.
To modulate fuel rail pressure, the ECM commands FPR cycling, depending on demand. If more fuel pressure is required, the ECM commands a lower FPR cycle. If less pressure is required, the ECM commands a higher FPR cycle. The ECM uses the fuel rail pressure sensor to continuously monitor fuel pressure.
If the ECM detects a problem, such as an unexpected increase or decrease in fuel pressure, or excessive or insufficient fuel pressure, that is, higher or lower than commanded, it will set diagnostic trouble code (DTC), DTC P0089 – “Fuel Pressure Regulator Performance,” and illuminate the malfunction indicator lamp (MIL). This is a generic DTC description, which means that automakers may use different descriptions.
Here are a few examples: Mitsubishi – Suction Control Valve Stuck Citroën – Fuel Rail Pressure Performance Ford – Fuel Pressure Relief Valve Open Chevrolet – Fuel Pressure Control Performance Information Codes 00, 11, 12, 18, and 19 indicate more specific faults