Deutz-Fahr M55 – Engine ECU (EMR): Engine Coolant Temperature Short Circuit

The engine control module has detected a short circuit in the coolant temperature sensor circuit (FMI 3: Short to +12V, FMI 4: Short to Ground). The controller receives an implausible voltage signal and cannot accurately determine the engine's operating temperature, which may lead to engine derating or default fueling strategies.

• Series 5
• 5D VSF TTV
• Virtus
• Nitro
• Agrofarm

1. 1

   Inspect the wiring harness running from the Engine ECU to the coolant temperature sensor for chafed insulation, pinched wires, or rubbing against the hot engine block.

2. 2

   Disconnect the sensor and inspect the electrical connector for water ingress, corrosion, or pushed-out/bent pins that could bridge connections.

3. 3

   With the battery disconnected and ECU harness unplugged, use a multimeter to test the sensor's signal wire for continuity to ground (chassis) or to the 12V power supply lines.

4. 4

   Measure the resistance across the pins of the coolant temperature sensor itself. If the multimeter reads 0 ohms, the sensor is internally shorted and must be replaced.

1. 1

   Preparation

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

2. 2

   Locate the Sensor

   Locate the coolant temperature sensor, which is threaded into the engine block or thermostat housing (its tip sits directly in the coolant passage).

3. 3

   Disconnect

   Unplug the electrical connector from the sensor.

4. 4

   Drain/Catch Coolant

   Place a clean catch pan under the engine. Be prepared for coolant to spill when the sensor is removed.

5. 5

   Remove the Sensor

   Use a deep socket or wrench to carefully unthread the faulty sensor from the block.

6. 6

   Install the New Sensor

   Thread the new OEM coolant temperature sensor into the housing. Tighten it to the manufacturer's specified torque (do not overtighten, as the brass threads can break).

7. 7

   Reconnect

   Plug the electrical harness back into the sensor, ensuring the locking tab clicks into place.

8. 8

   Refill Coolant

   Top off the engine coolant reservoir to replace any fluid lost during the swap.

9. 9

   Clear Codes

   Reconnect the battery and turn the ignition on. To permanently clear the history, you may need to use the Deutz SerDia diagnostic software.