Code No. P0683: Glow Control Unit Communication Abnormality




OPERATION



  • The electrical current source is supplied from the engine control relay connector terminal to the glow control unit connector terminal. Also, it is supplied from the glow control unit connector terminal to the body earth.
  • The request signal of operating the glow plug is input into the glow control unit connector terminal from the engine-ECU connector terminal G/CT.
  • The voltage for the glow plug is applied from the battery to the glow control unit connector terminal.
  • The voltage is applied from the glow control unit connector terminals to each glow plug.
  • The diagnosis signal is output from the glow control unit connector terminal to the engine-ECU connector terminal G/DA.

FUNCTION



  • The voltage applied to the glow control unit from the battery is applied to each glow plug in the duty ratio according to the signal from the engine ECU.

TROUBLE JUDGMENT


Check Conditions
  • While the engine is running
  • The electrical continuity duty to the glow plug is 17 - 83 %.
Judgment Criterion
  • The diagnosis signal is not received from the glow control unit for more than 5 seconds.

FAIL-SAFE AND BACKUP FUNCTION



  • The glow control is prohibited.
  • The EGR control is stopped (fully closed).

PROBABLE CAUSES



  • Failed glow control unit
  • Open/short circuit or harness damage in glow control unit power supply/earth circuit or loose connector contact.
  • Loose connector contact; open/short circuit or harness damage of communication wire between glow control unit and engine-ECU.
  • Failed engine-ECU

DIAGNOSTIC PROCEDURE


STEP 1. Perform voltage measurement at glow control unit connector.



  • Disconnect connector, and measure at harness side.
  • Ignition switch: ON
  • Voltage between terminal engine control relay side power supply line and body earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 2.

    Repair or replace the connector, or check and repair harness between glow control unit connector terminal and engine control relay connector terminal.

    • Check power supply line for open/short circuit.

STEP 2. Perform resistance measurement at glow control unit connector.



  • Remove the glow control unit, and measure the relay box side.
  • Resistance between terminal earthing line and body earth.
OK: Continuity (2 Ω or less)

Q. Is the check result normal?

Go to Step 3.

    Check and repair harness between glow control unit connector and body earth.

    • Check earthing line for open circuit and damage.

STEP 3. Check harness between glow control unit connector terminal and engine-ECU connector terminal G/CT.



  • Check signal 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.

STEP 4. Check harness between glow control unit connector terminal and engine-ECU connector terminal G/DA.



  • Check signal 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.

STEP 5. Check harness between glow control unit connector terminal and engine control relay connector terminal.



  • Check power supply line for damage.

Q. Is the check result normal?

Go to Step 6.
Repair or replace the connector, or repair the damaged harness wire.

STEP 6. M.U.T.-III diagnosis code.



  • Reconfirmation of diagnosis code.

Q. Is the diagnosis code set?

Go to Step 7.
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

STEP 7. Replace the glow control unit.



  • After replacing the glow control unit, reconfirm whether the diagnosis code is set.

Q. Is the diagnosis code set?

Replace the engine-ECU.
Check is end.