Code No. P0088: Common Rail High Pressure Malfunction


OPERATION



FUNCTION



  • The engine-ECU monitors the signals input from the rail pressure sensor.
  • Based on The input signals, the engine-ECU checks whether the fuel pressure in the common rail exceeds the maximum withstand pressure of the system.

TROUBLE JUDGMENT


Check Conditions
  • Rail pressure sensor is normal.
  • Battery positive voltage is 8 - 16 V.
Judgment Criterion
  • The rail pressure exceeds the threshold value of an abnormal high pressure for 3 seconds (continuous or accumulated).

FAIL-SAFE AND BACKUP FUNCTION



  • The throttle valve is closed (Fixed opening degree).
  • The rail pressure is controlled in the range between 50 and 60 MPa.
  • The DPF regeneration is prohibited.
  • The fuel injection amount is restricted (Output restriction).
  • The EGR control is stopped (fully closed).
  • The open angle of the accelerator pedal is restricted.
  • The AS&G control is prohibited.

PROBABLE CAUSES



  • Failed suction control valve
  • Failed engine-ECU

DIAGNOSTIC PROCEDURE

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

Q. Is any other diagnosis code than P0088 set?
Inspection chart for diagnosis codes (Refer to ).
Go to Step 2.

STEP 2. 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 3.
Repair or replace the connector, or replace the suction control valve.

STEP 3. Check harness between engine-ECU connector terminal SCV+ and suction control valve connector terminal.

  • Check power supply line for open/short circuit and damage.

Q. Is the check result normal?
Go to Step 4.
Repair or replace the connector, or repair the damaged harness wire then replace the common rail assembly and fuel injection tubes.

STEP 4. Check harness between engine-ECU connector terminal SCV- and suction control valve connector terminal.

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

Q. Is the check result normal?
Go to Step 5.
Repair or replace the connector, or repair the damaged harness wire then replace the common rail assembly and fuel injection tubes.

STEP 5. Perform output wave pattern measurement at suction control valve connector (Using an oscilloscope).

  • Use special tool test harness (MB991658) to connect connector, and measure at pick-up harness.
  • Engine: Idling
  • Connect the oscilloscope special patterns pickup to terminal engine-ECU SCV+ line 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 6.
Replace the suction control valve.

STEP 6. Replace the common rail assembly and fuel injection tubes.

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

Q. Does the trouble symptom persist?
Replace the engine-ECU.
The check is end.