Code No. P1272: Pressure Limiter Malfunction

OPERATION

Refer to Code No. P0191: Rail Pressure Sensor Range/Performance Problem
Refer to Code No. P0003: Suction Control Valve Open

FUNCTION

The engine-ECU controls the fuel discharge rate using the suction control valve.
The engine-ECU monitors the signals input from the rail pressure sensor.
The engine-ECU checks whether the pressure limiter valve is open, based on changes in the signals input from the rail pressure sensor (rapid drop of pressure after it goes extremely high).

TROUBLE JUDGEMENT

Check Conditions

Battery positive voltage is 8 - 16 V.
2 seconds later after the ignition switch has been in "ON" position or the engine has started up.
Engine speed is 600 r/min or more.
Rail pressure sensor is normal.

Judgement Criterion

After a pressure higher than the pressure of the pressure limiter opening valve is detected, fuel leakage diagnosis (supply pump discharge rate excessive) is detected within the predetermined time.

FAIL-SAFE AND BACKUP FUNCTION

The EGR control is stopped (fully closed).
The DPF regeneration is prohibited.
The throttle valve is opened (electrical discontinuity).

PROBABLE CAUSES

Failed suction control valve
Failed fuel system
Open/short circuit in suction control valve circuit or loose connector contact
Failed common rail assembly
Failed engine-ECU

DIAGNOSIS PROCEDURE

note

This diagnosis code is stored for an air penetration in the fuel line of the supply pump due to lack of fuel. Therefore, bleed air from the fuel line after the fuel supply, and delete the diagnosis code through M.U.T.-III. Repeat the cycle turning on the ignition switch and leaving it for 20 seconds to bleed air from the fuel line.

STEP 1. M.U.T.-III diagnosis code

Q. Is any other diagnosis code than P1272 output?

	Inspection chart for diagnosis codes (Refer to ).

	Go to Step 2.

STEP 2. Check the fuel filter contamination

Q. Is the check result normal?

	Go to Step 3.

	Replace the fuel filter then replace the common rail assembly and fuel injection tubes.

STEP 3. Release the air from the fuel line.

Repeat, more than 3 times, the cycle turning on the ignition switch and leaving it for more than 20 seconds. Operate the fuel pump in the fuel tank. Check there is no air at all in the fuel pipe.

Q. Does the trouble symptom persist?

	Replace the common rail assembly and common tubes.

	Go to Step 4.

STEP 4. Check suction control valve itself

Check suction control valve itself (Refer to ).

Q. Is the check result normal?

	Go to Step 5.

	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 <4N1> ).

STEP 5. Check of open circuit, short to earth, and damage in SCV+ line between engine-ECU connector and suction control valve connector.

Q. Is the check result normal?

	Go to Step 6.

	Repair the connector(s) or wiring harness then replace the common rail assembly and common tubes.

STEP 6. Check of open circuit, short to earth, and damage in SCV- line between engine-ECU connector and suction control valve connector.

Q. Is the check result normal?

	Go to Step 7.

	Repair the connector(s) or wiring harness then replace the common rail assembly and fuel injection tubes.

STEP 7. Perform output wave pattern measurement at engine-ECU connector (Using an oscilloscope).

(1)Disconnect engine-ECU harness, and connect special tool power plant ECU check harness (MB992291) to measure at connector for inspection.

(2)Engine: Idling

(3)Connect the oscilloscope special patterns pickup to engine-ECU connector (SCV+ terminal) and body earth.
OK: The waveform should show a pattern similar to the illustration of inspection procedure using an oscilloscope (Refer to ).

Q. Is the check result normal?

	Go to Step 8.

	Replace the engine-ECU.

STEP 8. Replace the common rail assembly and fuel injection tubes.

After replacing the common rail assembly and common tubes, re-check the trouble symptoms

Q. Does the trouble symptom persist?

	Replace the supply pump assembly. After replacing the supply pump, learn the supply pump (Refer to GROUP 00 - Precautions Before Service - What The Common Rail Engine Learns <4N1> ).

	The check is end.