4.2.54. SPN 157, FMI 0, Rail pressure above normal

Description

The measured rail pressure is over the critical limit. Measured pressure is > 1800bar. In normal conditions the pressure release valve (PRV) opens at a critical pressure (1800…2000 bar). In case PRV mechanical failure, ECU continuously monitors rail pressure and if measured pressure > 1800bar, engine will shutdown immediately.

Possible causes are: * high pressure pump wiring is defective * high pressure pump is not working correctly * Rail pressure sensor wiring is defective * The rail pressure sensor power supply is not correct * Rail pressure sensor is defective * Pressure release valve (PRV) is not working correctly

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 (1800bar), 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.
  • In case of damaged pressure release valve (PRV), high pressure pump or 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 sensor for reference.