John Deere 109 – ECU: Engine Coolant Pressure Signal Fault

The Engine Control Unit (ECU) has detected that the signal from the engine coolant pressure sensor is outside of its expected range. This anomaly may indicate a physical problem with the engine coolant pressure (such as a leak or low fluid) or an electrical issue with the component responsible for monitoring the pressure. The specific nature of the fault is often detailed by an accompanying Failure Mode Identifier (FMI), such as FMI 1 or 18 for low pressure, or FMI 31 for a signal failure.

• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 7R Series
• 8R Series
• 9R Series

1. 1

   Verify engine coolant level in the recovery tank and de-aeration tank when the engine is cool

2. 2

   Inspect the entire cooling system for external leaks, including hoses, radiator, water pump, and hose clamps

3. 3

   Pressure test the cooling system (typically to 10 psi or 0.7 bar) to check for internal leaks (such as a head gasket issue) or hidden external leaks

4. 4

   Inspect and pressure test the radiator cap to ensure it holds its rated specification

5. 5

   Check radiator fins for debris or blockages to ensure proper heat dissipation

6. 6

   Visually inspect the wiring harness and connector for the coolant pressure sensor for damage, corrosion, or loose connections

1. 1

   Address leaks and refill coolant

   If leaks are found during inspection or pressure testing, repair them by tightening hose clamps or replacing faulty hoses and components. Refill the cooling system with John Deere COOL-GARD II coolant.

2. 2

   Replace radiator cap

   If the radiator cap fails the pressure test, replace it with a new OEM part.

3. 3

   Test sensor and circuit

   If no leaks are present and the system holds pressure, use a diagnostic tool to read live data from the sensor. Test the sensor's circuit for correct voltage supply, ground, and signal output.

4. 4

   Replace coolant pressure sensor

   If the sensor or its signal is determined to be faulty, drain the coolant, remove the old sensor, install the new sensor, and refill the system.

5. 5

   Clear fault codes

   Use a diagnostic tool to clear active and stored fault codes from the ECU. Operate the machine to confirm the fault does not reappear.