John Deere ECU000676.05 – ECU: Glow Relay Output Problem

The Engine Control Unit (ECU) has detected an issue with the electrical output of the glow plug relay, indicating that the current is below the normal range or the circuit is open. The glow plug relay is a high-amperage switch that delivers power to heat the glow plugs. This output problem prevents the glow plugs from reaching the necessary temperature, which limits the operation of the cold start aid and can prevent the diesel engine from starting successfully in cold weather conditions.

• 2305
• 2320
• 2520
• 2720
• 4010
• 4100
• 4110
• 4115
• 17D
• 17G
• 17P
• 26G
• 26P
• 27D
• 35D
• 50D
• 304H
• 7210J
• Z-Trak Mowers
• Gator Utility Vehicles

1. 1

   Perform a visual inspection of the glow plug system components, checking the wiring harness and glow plugs for damage, corrosion, or loose connections.

2. 2

   Inspect fuses related to the glow plug circuit, including the main fuse (up to 50 amps, often located near the alternator) and related fuses in the main fuse panel.

3. 3

   Listen for the glow plug relay to click during the pre-heat cycle with the ignition on.

4. 4

   Test the glow plug relay coil resistance (terminals 85 and 86) with a multimeter; a good coil typically reads between 50 and 120 ohms.

5. 5

   Perform a continuity test on the relay's high-amperage terminals (30 and 87). There should be no continuity normally, but continuity should exist when 12V power is applied to the coil terminals.

6. 6

   Check for voltage at the glow plug wiring harness when the ignition is in the 'on' or 'pre-heat' position; it should be close to battery voltage.

7. 7

   Test each glow plug for continuity and resistance (typically between 0.5 and 2 ohms). An infinite resistance reading indicates a faulty glow plug.

1. 1

   Ensure safety

   Park the machine on a level surface, turn it off, and disconnect the negative battery terminal to prevent electrical shorts.

2. 2

   Address immediate electrical faults

   If diagnostic checks revealed a blown fuse, replace it with one of the exact same amperage rating. Repair or replace any damaged sections of the wiring harness.

3. 3

   Replace faulty glow plug relay

   If the relay failed the resistance or continuity tests, replace it with a new unit. The relay is often located in a main relay box, behind the operator's seat, or under the hood.

4. 4

   Replace faulty glow plugs

   If one or more glow plugs have infinite resistance, replace them (replacing as a full set is recommended). Apply penetrating oil before removal if seized. Thread new plugs in by hand and tighten to the manufacturer's specified torque (often around 12-15 ft-lbs).

5. 5

   Reassemble and test

   Reconnect the negative battery terminal. Turn the ignition to the 'on' position to allow the glow plug cycle to run, then start the engine to confirm the repair has been successful and the fault code does not reappear.