Posted in MMC L200

P1272 – Pressure Limiter Malfunction MMC L200 IV

 Posted by  Posted on September 29, 2020

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 JUDGMENT

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

    • PROBABLE CAUSES

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

    • DIAGNOSIS PROCEDURE

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

    Q. Is any other diagnosis code than P1272 set?

    STEP 2. Check the fuel filter contamination

    Q. Is the check result normal?

    STEP 3. Release the air from the fuel line.

  • After releasing the air from the fuel line, continue idle operation for about five minutes and recheck for abnormal symptoms.

    • Q. Does trouble symptom persist?

    STEP 4. Check suction control valve itself

    Q. Is the check result normal?

    STEP 5. Connector check: C-103 engine-ECU connector and A-47 suction control valve connector

    Q. Are the check results normal?

    STEP 6. Check harness between C-103 (terminal No. 131) engine-ECU connector and A-47 (terminal No. 1) suction control valve connector.

  • Check output line for open/short circuit and damage.

    • Q. Is the check result normal?

    STEP 7. Check harness between C-103 (terminal No. 146) engine-ECU connector and A-47 (terminal No. 2) suction control valve connector.

  • Check output line for open/short circuit and damage.

    • Q. Is the check result normal?

    STEP 8. Perform output wave pattern measurement at A-47 suction control valve (Using an oscilloscope).

  • Engine: Idling
  • Connect the oscilloscope special patterns pickup to engine-ECU terminal No. 131 and earth.

    • Q. Is the check result normal?

    STEP 9. 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 trouble symptom persist?

    Author: admin