Code No. P0191: Rail Pressure Sensor Range/Performance Problem




OPERATION



  • 5 V power is supplied from the engine-ECU (terminal No. 70) to the rail pressure sensor (terminal No. 1).
  • The rail pressure sensor (terminal No. 3) is earthed to the engine-ECU (terminal No. 88).
  • Sensor signals are input from the rail pressure sensor (terminal No. 2) to the engine-ECU (terminal No. 64).

FUNCTION



  • The engine-ECU monitors the signals input from the rail pressure sensor.
  • Based on these signals, the engine-ECU checks the rail pressure sensor for errors.

TROUBLE JUDGMENT


Check Condition
  • Engine is running.
Judgment Criterion
  • A difference between the objective and actual rail pressures exceeds 15 MPa for 0.5 second, and the rail pressure sensor has an output voltage variation of 0.01 V or less.

PROBABLE CAUSES



  • Failed rail pressure sensor
  • Failed suction control valve
  • Fuel line blocked
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Check suction control valve itself.

  • Check suction control valve itself (Refer to ).

Q. Is the check result normal?
Go to Step 2.
Replace the suction control valve. After replacing the suction control valve, learn the supply pump (Refer to GROUP 00 - Precautions Before Service - What The Common Rail Engine Learns ).

STEP 2. Connector check: A-44 rail pressure sensor connector.

Q. Is the check result normal?

Go to Step 3.

Repair or replace the connector.

STEP 3. Connector check: C-105 engine-ECU connector

Q. Is the check result normal?

Go to Step 4.

Repair or replace the connector.

STEP 4. Check harness between A-44 (terminal No. 3) rail pressure sensor connector and C-105 (terminal No. 88) engine-ECU connector.


note Before checking harness, check intermediate connector A-131, and repair if necessary.

  • Check earthing line for damage.

Q. Is the check result normal?

Go to Step 5.

Repair the damaged harness wire.

STEP 5. Check harness between A-44 (terminal No. 1) rail pressure sensor connector and C-105 (terminal No. 70) engine-ECU connector.


note Before checking harness, check intermediate connector A-131, and repair if necessary.

  • Check power supply line for damage.

Q. Is the check result normal?

Go to Step 6.

Repair the damaged harness wire.

STEP 6. Check harness between A-44 (terminal No. 2) rail pressure sensor connector and C-105 (terminal No. 64) engine-ECU connector.


note Before checking harness, check intermediate connector A-131, and repair if necessary.

  • Check output line for damage.

Q. Is the check result normal?

Go to Step 7.

Repair the damaged harness wire.

STEP 7. Perform voltage measurement at A-44 rail pressure sensor connector.


  • Use special tool test harness (MB991658) to connect connector, and measure at pick-up harness.
  • Engine: Idling (after warning up)
  • Voltage between terminal No. 2 and earth.
OK: 1.15 - 1.75 V

Q. Is the check result normal?

Replace the engine-ECU. When the engine-ECU is replaced, write the chassis number (Refer to GROUP 00 - Precautions Before Service - How to Perform Chassis Number Writing ). After replacing the engine-ECU, register the injector identification code and learn fuel injection (Refer to GROUP 00 - Precautions Before Service - What The Common Rail Engine Learns ). After registering the injector identification code, the vehicle equipped with the DPF carries out the forcible DPF regeneration. (Refer to GROUP 17 - Emission Control - Diesel Particulate Filter (DPF) System - Forcible DPF Regeneration ).

Replace the common rail assembly and fuel injection tubes.