New Holland ENG 3689 – Engine Controller (Engine ECU / EDC): Glow Plugs: DFC for Faulty Diagnostic Data Transmission or Protocol Error

Communication failure or wrong data transmission between the Glow Plug Control Unit (GCU) and the Engine Controller. The engine ECU is expecting specific protocol data from the glow plug module over the communication bus, but the data is either missing, corrupted, or formatted incorrectly.

• F5C
• F5H
• ISM-DI
• L220
• L230
• SR175
• B90B
• B100B
• 586H
• 588H
• Farmall 45C

1. 1

   Visually inspect the wiring harness connecting the Engine ECU to the Glow Plug Control Unit for chafed wires, pinched harnesses, or heat damage.

2. 2

   Disconnect the harnesses at both the ECU and the GCU and inspect the pins for corrosion, moisture ingress, or pushed-out pins.

3. 3

   Use a multimeter to test the communication lines (CAN/LIN bus) between the GCU and the Engine ECU for continuity. Verify that the lines are not shorted to ground or shorted to battery voltage.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the negative battery terminal to prevent electrical spikes.

2. 2

   Clean and Reseat Connectors

   If the diagnostic checks reveal dirty or loose connections at the Glow Plug Control Unit, clean the contacts with electrical contact cleaner, apply dielectric grease, and securely reconnect the harness.

3. 3

   Repair Wiring

   If a break or short is found in the communication wires during the continuity test, repair the damaged section of the wiring harness using OEM-approved splicing methods, or replace the harness section.

4. 4

   Clear Codes

   Reconnect the battery, turn the key to the ON position, and use a diagnostic service tool to clear the ENG 3689 fault code.

5. 5

   Test Operation

   Cycle the key and start the engine. Monitor the diagnostic tool to see if the code returns.

6. 6

   Replace the Module

   If the wiring is fully intact and the fault code persists immediately upon key-on, the internal communication circuitry of the Glow Plug Control Unit has failed. Replace the Glow Plug Control Unit.