John Deere 676.05 – ECU (Engine Control Unit): Cold Start Aid Circuit Has High Resistance / Glow Plug Relay Out of Range Low / Glow Plug Relay Voltage Too Low

This fault is triggered when the Engine Control Unit (ECU) detects that the cold start aid relay output is low (passive) or has an open circuit/high resistance when the ECU is actively commanding the relay to energize.

• 5085E
• 5090E
• 5090EL
• 5100E
• 5085M
• 5100M
• 5100MH
• 5100ML
• 5115ML
• 5090M
• 5115M
• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 5M Series (5085M, 5095M, 5105M)
• 6030 Series (6230, 6330, 6430)
• 7030 Series (7630, 7730, 7830, 7930)
• 1025R
• 748H Skidders
• 4WD Loaders
• Excavators
• PowerTech 2.4L, 3.0L, 4.5L, 6.8L, and 9.0L diesel engines

1. 1

   Relay Circuit Test: Locate the Glow Plug Relay (often designated as relay K03 or K22) and test to see if it clicks and properly closes the circuit when voltage is applied.

2. 2

   Wiring and Connector Inspection: Check the wiring harness between the ECU and the glow plug relay for open circuits, chafing, or corrosion. Specifically check the ECU connectors (e.g., ICC-J3 connector).

3. 3

   Voltage Drop Test: Verify that the relay is receiving proper supply voltage and that the ECU is successfully sending the ground/command signal to the relay coil.

1. 1

   Disconnect battery

   Disconnect the negative battery terminal to ensure safety while working on the electrical system.

2. 2

   Access load center

   Access the main fuse and relay load center (location varies by model, often in the cab console or under the hood).

3. 3

   Remove relay

   Remove the suspect Glow Plug Relay (K03/K22).

4. 4

   Inspect terminals

   Inspect the relay socket terminals for spread pins, corrosion, or signs of melting. Clean the terminals with electrical contact cleaner if necessary.

5. 5

   Replace relay

   If the relay failed the diagnostic bench test, install a new OEM glow plug relay.

6. 6

   Repair wiring

   If the relay is functional, repair any broken or highly resistant wires in the harness connecting the ECU to the relay.

7. 7

   Clear codes

   Reconnect the battery, cycle the key to power the tractor, and clear the stored fault codes.

8. 8

   Verify repair

   Perform a cold start to verify the code does not return and the cold start aid functions normally.