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, and the rail pressure sensor has an output voltage variation of 0.01 V or less.

FAIL-SAFE AND BACKUP FUNCTION



  • The rail pressure is controlled in the range between 50 and 100 MPa.
  • The fuel injection amount is restricted (Output restriction).
  • The open angle of the accelerator pedal is restricted.
  • The throttle valve is closed (Fixed opening degree).
  • The EGR control is stopped (fully closed).
  • The DPF regeneration is prohibited.
  • The AS&G control is prohibited.

PROBABLE CAUSES



  • Failed rail pressure sensor
  • Harness damage in rail pressure sensor circuit or loose connector contact
  • Failed suction control valve
  • Failed engine-ECU

DIAGNOSTIC 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.

STEP 2. Connector check: B-01 rail pressure sensor connector.

Q. Is the check result normal?
Go to Step 3 .
Repair or replace the connector.

STEP 3. Connector check: B-09 engine-ECU connector

Q. Is the check result normal?
Go to Step 4 .
Repair or replace the connector.

STEP 4. Check harness between B-01 (terminal No. 3) rail pressure sensor connector and B-09 (terminal No. 88) engine-ECU connector.

  • 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 B-01 (terminal No. 1) rail pressure sensor connector and B-09 (terminal No. 70) engine-ECU connector.

  • 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 B-01 (terminal No. 2) rail pressure sensor connector and B-09 (terminal No. 64) engine-ECU connector.

  • 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 B-01 rail pressure sensor connector.

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

Q. Is the check result normal?
Replace the engine-ECU.
Replace the common rail assembly and fuel injection tubes.