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


OPERATION



  • 5 V power is supplied from the engine-ECU connector terminal FPS5 to the rail pressure sensor connector terminal.
  • The rail pressure sensor connector terminal is earthed to the engine-ECU connector terminal FPSE.
  • Sensor signals are input from the rail pressure sensor connector terminal to the engine-ECU connector terminal FPS.

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.

  • Suction control valve connector check.
  • Check suction control valve itself (Refer to ).

Q. Is the check result normal?
Go to Step 2.
Repair or replace the connector, or replace the suction control valve.

STEP 2. Check harness between rail pressure sensor connector terminal and engine-ECU connector terminal FPSE.

  • Check earthing line for damage.

Q. Is the check result normal?
Go to Step 3.
Repair or replace the connector, or repair the damaged harness wire.

STEP 3. Check harness between rail pressure sensor connector terminal and engine-ECU connector terminal FPS5.

  • Check power supply line for damage.

Q. Is the check result normal?
Go to Step 4.
Repair or replace the connector, or repair the damaged harness wire.

STEP 4. Check harness between rail pressure sensor connector terminal and engine-ECU connector terminal FPS.

  • Check output line for damage.

Q. Is the check result normal?
Go to Step 5.
Repair or replace the connector, or repair the damaged harness wire.

STEP 5. Perform voltage measurement at 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 engine-ECU FPS line and body 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.