Massey Ferguson 109.03 – Engine ECU / EEM (Electronic Engine Management): Coolant Pressure Sensor Signal Voltage High

The Engine Control Unit has detected that the voltage signal returning from the coolant pressure sensor is exceeding the normal operating range. This condition is typically caused by either an open circuit (a broken wire or disconnected plug) or a short circuit to a high voltage source (such as a 5V or 12V line).

• 4710
• 7724S
• 5712SL
• Interim Tier 4 (2012-2015)
• 7722
• 7722S
• 7615
• 5613
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 7616
• 7618
• 5608
• 4708
• 7619
• 7626
• 7726S
• 7624
• 4707
• 4709
• 5711SL
• 7614
• 7718S
• 5610
• 7620
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 5612
• 7622
• 7720
• Tier 4 (2015-2021)
• 5611
• 7715S
• 5609
• 7724
• 8600 Series

1. 1

   Visually inspect the coolant pressure sensor connector and wiring harness for physical damage, corrosion, or backed-out pins.

2. 2

   Disconnect the sensor, turn the key ON (engine off), and measure the voltage at the sensor connector between the 5V reference supply pin and the ground pin (should read exactly 5Vdc).

3. 3

   Check the signal wire for continuity back to the EEM controller and ensure it is not shorted to the 5V reference wire or the 12V battery supply.

4. 4

   If the wiring tests good, plug in a known-good replacement coolant pressure sensor to see if the active fault code clears.

1. 1

   Power Down

   Turn off the tractor and remove the key.

2. 2

   Locate the Sensor

   Locate the coolant pressure sensor, which is typically mounted on the expansion tank or near the coolant pump/thermostat housing depending on the specific Sisu engine variant.

3. 3

   Repair Wiring

   If your diagnostic checks revealed a broken wire or a short to power, repair the affected section of the engine harness and replace the connector pigtail if necessary.

4. 4

   Replace the Sensor

   If the wiring is intact, the sensor itself has failed internally. Relieve any residual pressure in the cooling system by carefully loosening the expansion tank cap (ensure the engine is cool). Unplug the electrical connector. Unthread the faulty coolant pressure sensor. Install the new sensor and tighten to OEM specifications. Reconnect the electrical harness.

5. 5

   Clear Codes

   Turn the ignition ON and use a diagnostic service tool (like WinEEM3/4 or an AGCO diagnostic tool) to clear the stored fault codes.

6. 6

   Verify Repair

   Start the engine, allow it to reach operating temperature, and verify that the warning lamp remains off and the code does not return.