Deutz-Fahr I35 – Engine Control Unit (Engine ECU): Power output 1 short circuit to battery or open circuit

The system detects that the power output to the preheating relay is either disconnected (open circuit) or shorted to the +12V battery voltage. Because of this, the engine's cold-start preheating function is disabled or compromised.

• Agroplus 310, 320, 410, and 420 Profiline series tractors
• Deutz-Fahr Series 5
• Deutz-Fahr Series 5D VSF TTV
• Agrofarm Series
• Agrotron Series

1. 1

   Verify that the preheating relay is receiving proper +12V power from the battery/fuse block at the relay power pin.

2. 2

   Test the control pin from the Engine ECU to the relay to ensure the ECU is actively grounding/commanding the relay during the ignition 'ON' preheating phase.

3. 3

   Verify if the preheating relay is stuck in the closed or open position.

4. 4

   Check the resistance of the preheating resistor/glow plugs and the wiring harness.

5. 5

   Measure the resistance on the feedback line to the ECU to ensure there is no open circuit or short to battery voltage.

1. 1

   Safety First

   Turn off the tractor, remove the ignition key, and disconnect the negative battery terminal to prevent accidental shorts.

2. 2

   Locate the Preheating Relay

   Access the main electrical fuse/relay plate (usually located in the cab console or engine bay compartment, depending on the model).

3. 3

   Inspect the Wiring Loom

   Examine the preheating wiring loom for chafing, melted insulation, or disconnected plugs. Pay special attention to the connector at the relay base.

4. 4

   Test/Replace the Relay

   Remove the preheating relay. Use a multimeter to test the coil resistance. Apply 12V to the coil pins and listen for a solid "click," then verify continuity across the load pins. If the relay fails this test, is burnt, or is stuck open/closed, it must be replaced.

5. 5

   Repair Wiring (If Applicable)

   If the relay is functional but the code persists, trace the wire from the relay output to the engine preheating flange/glow plugs. Repair any broken wires (open circuit) or wires rubbed bare against the chassis (short to battery).

6. 6

   Reassembly and Clearing

   Reinstall the relay, reconnect the battery, and turn the ignition key to position I (Preheating). Verify that the preheating indicator light on the instrument panel illuminates and then turns off correctly. Clear the fault codes using the SERDIA diagnostic tool if the code is stored as a hard fault.