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 JUDGEMENT
Check Conditions
- While the engine is running
- The electrical continuity duty to the glow plug is 17 - 83 %.
Judgement 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
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STEP 1. Voltage measurement at glow control unit connector (power supply line).
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(1)Disconnect connector, and measure at harness side.
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(3)Check the voltage between the glow control unit connector (power supply line) and body earth.
OK: System voltage
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Q.
Is the check result normal?
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 Go to Step 2.
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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.
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STEP 2. Resistance measurement at glow control unit connector (body earth line).
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(1)Remove the glow control unit, and measure at the relay box side.
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(2)Measure the resistance between the glow control unit connector (body earth line) and body earth.
OK: Continuity (2 Ω or less)
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Q.
Is the check result normal?
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Go to Step 3.
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Repair body earth line between glow control unit connector and body earth.
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STEP 3. Check of open circuit, short to earth, and damage in G/CT line between glow control unit connector and engine-ECU connector.
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Q.
Is the check result normal?
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Go to Step 4.
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Repair the connector(s) or wiring harness.
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STEP 4. Check of open circuit, short to earth, and damage in G/DA line between engine-ECU connector and glow control unit connector.
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Q.
Is the check result normal?
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Go to Step 5.
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Repair the connector(s) or wiring harness.
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STEP 5. Check of damage in power supply line between engine control relay connector and suction glow control unit.
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Q.
Is the check result normal?
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Go to Step 6.
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Repair the connector(s) or wiring harness.
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STEP 6. M.U.T.-III diagnosis code.
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- Reconfirmation of diagnosis code.
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Q.
Is the diagnosis code set?
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Go to Step 7.
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Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions).
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STEP 7. Replace the glow control unit.
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- After replacing the glow control unit, reconfirm whether the diagnosis code is set.
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Q.
Is the diagnosis code set?
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Replace the engine-ECU.
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Check is end.
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