John Deere 000676.31 – ECU: Cold Start Circuit Has Voltage When It Should Be Switched Off

The Engine Control Unit (ECU) has detected voltage in the glow plug circuit when it should be de-energized. This typically indicates that the glow plug relay is mechanically stuck in the closed position or a short circuit is providing continuous power to the circuit. If left unresolved, this condition can drain the battery, cause premature failure of the glow plugs, and restrict the function of the cold start aid system.

• Tractors
• Utility Vehicles
• Mowers
• Gator
• Compact Tractors

1. 1

   Visually inspect the glow plug relay, wiring harness, and connectors for signs of corrosion, damage, or loose connections

2. 2

   Verify battery voltage and load-test the battery, as low voltage can cause electrical issues. Check all related fuses to ensure they are intact

3. 3

   Listen for an audible click from the relay when the key is turned to the 'on' or 'start' position to verify the control circuit is functioning

4. 4

   Test voltage at the relay control circuit (should be 12V when commanded on) and power circuit (should be 0V with key off; 12V indicates a stuck relay or short to power)

5. 5

   Disconnect the wiring harness from the relay and glow plugs to check for continuity and shorts to ground or power using a multimeter

1. 1

   Disconnect battery

   Disconnect the negative battery terminal to prevent short circuits before starting electrical repairs.

2. 2

   Replace glow plug relay

   If diagnostics indicate a faulty or stuck relay, locate it (often on the firewall or near the engine block) and replace it with a new OEM part.

3. 3

   Repair or replace wiring

   If the wiring harness is damaged, corroded, or shorted, repair or replace it. Ensure all connections are clean and secure.

4. 4

   Clear fault codes

   Reconnect the battery, start the engine, and use the machine's diagnostic display or service tool to clear the fault code.

5. 5

   Verify repair

   Operate the machine and cycle the key and cold start system multiple times to ensure the relay is functioning correctly and disengaging as expected.