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

OPERATION

5 V power is supplied from the engine-ECU terminal (No. 81) to the rail pressure sensor terminal (No. 1).
The rail pressure sensor terminal (No. 3) is grounded to the engine-ECU terminal (No. 76).
Sensor signals are input from the rail pressure sensor terminal (No. 2) to the engine-ECU terminal (No. 56).

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 supply pump assembly.

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) crank angle sensor connector and C-105 (terminal No. 76) engine-ECU connector.

note

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

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) crank angle sensor connector and C-105 (terminal No. 81) engine-ECU connector.

note

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

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. 56) engine-ECU connector.

note

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

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 - 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

Replace the common rail assembly and fuel injection tubes.