2.2.57. SPN 157, FMI 15, Rail pressure monitoring: Positive pressure deviation.ΒΆ

Description

The EEM4 monitoring system has detected a positive deviation in the rail pressure. The measured rail pressure is not increasing according to the setpoint value to the MPROP. Typically this indicates a leakage in the injector or elsewhere on the high pressure side.

NOTE: Due to the very high injection pressure, there is a serious risk for injury during engine running, if there is a leakage on the high pressure side.

Possible causes are:

  • Air in the fuel on the high pressure side (empty tank).
  • The injector is not working correctly (internal leakage).
  • The pressure relief valve is not working properly (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 (external leakage).
  • The rail pressure sensor wiring is defective.

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 an active fault. The engine functions dependent on the rail pressure are not active.

Solution

First save the error log and then do the procedure that follows:

  • A temporary pressure peak (breakdown) during engine running. For example an abnormal load drop/fuel quantity drop during running. If the fault does not activate within the next 10 operating hours, the cause was probably a too sensitive diagnostic function.

Solution2: Turn the ignition key off and then back on. Start the engine; if the fault code is still active when the engine is running, check the following paths:

  • Stop the engine. Examine the engine high pressure pipes etc. visually for a possible leakage.
  • Examine the tightness of the injector side feed pipes. The correct torque tightening and operating instructions can be found in the engine repair manual.
  • Examine 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.
  • Test the nozzle operation with the Service Tool test function, or have the injectors inspected by an authorized Bosch service dealer.
  • Test the high pressure pump operation with the Service Tool test function. If test results show a leakage in the high pressure pump, the defective part can be the high pressure pump or the MPROP solenoid valve.
  • In case of damaged injector, pressure relief valve, high pressure pipe, rail pressure sensor or a wiring harness, replace the damaged parts according to the instructions in the service manual.
  • Examine the rail pressure sensor wiring, the connectors and the contact surfaces of the connector pins (possible oxidation).
  • Make sure that the 5 V power supply to the rail pressure sensor is correct.
  • Try the operation with another rail pressure sensor to see if the sensor is defective.

See Rail pressure sensor for reference.