3.2.335. SPN 520320, FMI 31, Rail Pressure control: Pressure ABOVE normal in limp home modeΒΆ

Description

The measured rail pressure is over the critical limit. Measured pressure is > 2125bar. In case of a pressure control valve mechanical failure, the EEM4 system continuously monitors the rail pressure, and if the measured pressure is >2150bar, the engine will shutdown immediately.

Possible causes are:

  • The pressure control valve is not working correctly (stuck).
  • The pressure control valve wiring is defective.
  • The high pressure pump is not working correctly.
  • The high pressure pump wiring is defective.
  • The rail pressure sensor wiring is defective.
  • The rail pressure sensor power supply is not correct.
  • The rail pressure sensor is defective.
  • The zero delivery throttle is clogged.
  • The pressure before the high pressure pump is too high (e.g. in the case of an electric presupply pump with a pressure relief valve).
  • The pressure after the zero delivery throttle too high.

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.

NOTE: Due to the very high injection pressure (> 2000bar), there is a serious risk for injury during engine running, if the high pressure side has a leakage.

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:

  • Check the high pressure pump: Look for possible high pressure pump faults and inspect them accordingly (e.g. faults with the wiring and the connectors).
  • Check the high pressure pump operation with the Service Tool test function, or have the pump inspected by an authorized Bosch service dealer.
  • 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 control valve: Look for possible valve stucks and inspect them accordingly (e.g. faults with the wiring and the connectors).
  • Check the electric presupply pump: Look for possible relief valve stucks and inspect them accordingly (e.g. faults with the wiring and the connectors).
  • In case of a damaged pressure control valve (PCV), high pressure pump or a wiring harness, replace the damaged parts according to the instructions in the service manual.

NOTE: The high pressure part removal, inspection and replacement should be performed only by qualified injection system service personnel. Special instructions may apply.

See Rail pressure sensor for reference.