3.2.304. SPN 520233, FMI 31, Rail pressure below normalΒΆ

Description

The EEM4 monitoring system has detected too low pressure in fuel high pressure common rail.

Possible causes are:

  • Air in the fuel on the high pressure side (e.g. an empty tank).
  • The injector is not working correctly (an internal leakage).
  • The fuel side feed pipes are leaking (an internal leakage).
  • The pressure relief valve is not working properly (a leakage).
  • The high pressure pump is not working properly.
  • The MPROP solenoid valve in the high pressure pump is not working properly (defective).
  • There is a leakage on the high pressure side (an external leakage).
  • The rail pressure sensor wiring is defective.
  • The fuel filters are full.

Reaction in EEM

The FC is stored and the warning lamp is activated. Engine power is heavily reduced (Degradation Level 3). The CAN message indicates active fault. The engine functions dependent on the rail pressure are not active.

Solution

First save the error log and then erase it. Restart the ECU after erasing the error log. If the fault occurs again during the next driving cycle, check the following paths:

  • Stop the engine. Check the engine high pressure pipes etc. visually for a possible leakage.
  • Check the rail pressure sensor wiring, the connectors and the contact surfaces of the connector pins (possible oxidation).
  • Check the 5 V power supply to the sensor.
  • Check the operation with another rail pressure sensor to see if the sensor is defective.
  • Check the pressure relief valve visually for impurities. If there are impurities, clean the valve or replace it with a new one. Tighten the valve according to the instructions in the service manual.
  • Check the nozzle operation with the Service Tool test function, or have the injectors inspected by an authorized Bosch service dealer.
  • Check the high pressure pump operation with the Service Tool test function. If test results show a leakage on the high pressure pump, the defective part can be the high pressure pump or the MPROP solenoid valve.
  • In case of a damaged injector, pressure relif valve, high pressure pipe, rail pressure sensor or a wiring harness, replace the damaged parts according to the instructions in the service manual.
  • The fuel filter service. The filters are full and need to be changed.

Solution2: Valid only for 4-valve engines.

  • Check the tightness of the injector side feed pipes. The correct torque tightening and operating instructions can be found in the engine repair manual.

See Rail pressure sensor for reference.