New Holland 3691 – Engine ECU: Glow Plugs No Load Error

The Engine Control Unit (ECU) has activated the glow plug circuit but does not detect the expected electrical current draw. This indicates an open circuit preventing the glow plugs from receiving power, which may affect engine start performance, causing hard starting or failure to start in cold weather, potentially accompanied by white exhaust smoke due to unburned fuel.

• L230
• T4.110F
• T4 Series
• T5 Series
• Workmaster Series
• Boomer Series
• L225
• T4.55
• T4.110
• TC Series
• TC35
• TC40
• TC45
• L454
• L455
• L553
• L555
• T1510
• T2210
• L125
• L160
• L170
• LS160
• LS170

1. 1

   Check for blown fuses in the glow plug circuit (e.g., 10-amp fuse F16 on some models)

2. 2

   Inspect the wiring harness and connectors leading to the glow plug relay/module and glow plugs for damage, corrosion, or melted connectors

3. 3

   Test battery voltage (ensure it is above 12.6V) and verify main chassis and engine ground connections are clean and tight

4. 4

   Test glow plug resistance using a multimeter (measure between terminal and engine block). Expected resistance is 0.5 to 2.0 ohms; an 'OL' reading indicates a failed, open glow plug

5. 5

   Test the glow plug relay or control module. For relays, listen for a click and measure battery voltage at the output terminal when the key is on. For control modules, verify individual glow plug monitoring wires

1. 1

   Resolve preliminary electrical faults

   Replace any blown fuses, clean and tighten ground connections, and repair damaged wiring or connectors found during inspection.

2. 2

   Replace faulty glow plugs

   If glow plugs show an open circuit ('OL' resistance), replace them as a complete set. Clean cylinder head threads, apply anti-seize, and torque to 12-15 ft-lbs (verify with service manual).

3. 3

   Replace glow plug relay or control module

   If the relay fails to output voltage or the control module is faulty, disconnect the negative battery terminal, replace the unit, and reconnect.

4. 4

   Clear codes and verify

   Clear the fault codes using a diagnostic tool. Start the engine to verify the code does not return and cold starting is smooth.