John Deere 676.03 – ECU: Glow Plug Relay Voltage High

The Engine Control Unit (ECU) has detected a high voltage on the glow plug relay output circuit at a time when the ECU is not commanding the relay to be active. This indicates that the relay may be stuck in the closed position, sending continuous power to the glow plugs, or that the output circuit is shorted to a power source. This condition affects the proper operation of the engine's glow plug system, which is critical for starting the engine in cold conditions.

• 5065M
• 5075M
• 5085M
• 5095M
• 5095MH
• 5105M
• 5015ML
• 5100M
• 5115M
• 7630
• 7730
• 7830
• 7930
• 7810

1. 1

   Remove the glow plug relay and perform a continuity test across the high-current load terminals. Continuity while unpowered indicates welded contacts (stuck relay).

2. 2

   Inspect the wiring harness between the ECU and the glow plug relay for melted insulation, chafing, or a short-to-battery voltage on the diagnostic feedback wire.

3. 3

   Inspect the glow plug relay fuse jumper for signs of excessive heat or melting.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the negative battery cable to prevent electrical shorts or accidental sparks.

2. 2

   Locate the Relay

   Locate the glow plug relay. Depending on the model, it is typically mounted on a harness bracket directly on the engine block, or near the engine fuse panel.

3. 3

   Remove the Faulty Relay

   Disconnect the wiring harness connector (or unbolt the ring terminals, depending on the relay style) from the relay. Unbolt the relay from its mounting bracket.

4. 4

   Install the New Relay

   Secure the replacement OEM glow plug relay to the mounting bracket.

5. 5

   Reconnect Wiring

   Reconnect the wiring harness, ensuring the connector is fully seated and locked. If the harness connector shows signs of melting due to the continuous current draw, the harness (or pigtail) must also be replaced.

6. 6

   Test the System

   Reconnect the negative battery cable. Turn the key to the ON position. The cold start/glow plug indicator light on the dash should illuminate temporarily and then turn off.

7. 7

   Clear Codes

   Start the engine and use the CommandCenter or a diagnostic scanner to clear the stored 000676.03 code. Verify the code does not return.