Fuel Pressure Regulation, Diagnostics (Only Vehicles With Demand Controlled Fuel Pumps)

General 

The fuel pump control module has no functions for diagnostics. Fuel pressure regulation components and functions are diagnosed by the engine control module (ECM).

• Fuel pump control module  , the power supply is checked. A diagnostic trouble code (DTC) will be stored and the fuel pump will not work if there is no power supply to the fuel pump control module
• Fuel pressure sensor with temperature sensor  , the pressure and temperature signals are checked to see if they are outside the normal operating range of the sensor. If a fault in the fuel pressure sensor is detected, the fuel pump (FP) will run at full power and the pressure is governed by the by-pass valve in the fuel tank
• Fuel pressure  , the engine control module (ECM) compares the requested pressure with the measured pressure (the signal from the fuel pressure sensor). If the measured pressure deviates excessively from the requested pressure, or if the pressure pulses, a diagnostic trouble code (DTC) will be stored for incorrect fuel pressure. The diagnostic is not active if a diagnostic trouble code (DTC) for the fuel pressure sensor is stored. A diagnostic trouble code (DTC) for fuel pressure will be stored if there is a fault in the fuel pump 
• Communication cable.  The engine cannot be started if there is a fault in the communication cable between the engine control module (ECM) and the fuel pump control module. A diagnostic trouble code (DTC) will be stored for the fault.

For further information about diagnostic trouble codes (DTCs), see Information, diagnostic trouble codes (DTCs) in appropriate diagnostics tool.

Components/functions which cannot be diagnosed: 

If there is a fault in the by-pass valve  in the tank unit, the starting process of the engine will take longer if the valve is leaking fuel when the fuel pump is off. If the valve does note open when there are pressure peaks in the fuel system, engine operation will be negatively effected, especially after engine braking.