John Deere 000109.18 – ECU: Coolant Pressure Is Low

The Engine Control Unit (ECU) has detected low pressure in the engine's sealed cooling system. This can be caused by coolant leaks, a faulty pressure cap, or a malfunctioning pressure sensor. The system relies on pressure to raise the boiling point of the coolant for efficient heat transfer. A loss of pressure compromises this capability, causing the ECU to trigger an engine power derate to prevent potential damage from overheating. Immediate attention to this fault is recommended.

• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6165M
• 6175M
• 6180M
• 6185M
• 6195M
• 6200M
• 6220M
• 6230M
• 6240M
• 6250M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 6R 145
• 6R 155
• 6R 165
• 6R 175
• 6R 185
• 6R 195
• 6R 215
• 6R 230
• 6R 250
• 7R Series
• 8R Series
• 8RT Series
• 9R Series
• 9RT Series
• 9RX Series
• R430

1. 1

   Check the coolant level in the de-aeration tank and recovery tank (low level is the most straightforward cause).

2. 2

   Visually inspect all cooling system hoses, the radiator, and the water pump for any signs of external leaks, such as wetness, dried white or greenish coolant residue, or damage.

3. 3

   Perform a radiator cap test using a cooling system pressure tester (e.g., D05104ST) to ensure the cap holds its specified pressure rating steady for at least 10 seconds.

4. 4

   Perform a cooling system pressure test with the engine off and cool to check the integrity of the entire system. If pressure drops but no external leaks are found, suspect an internal leak such as a faulty EGR cooler or head gasket.

5. 5

   Inspect the coolant pressure sensor's wiring and connector for damage or corrosion. If the system holds pressure and the cap is good, test the sensor using John Deere Service ADVISOR or a multimeter.

1. 1

   Address coolant leaks

   If the pressure test revealed external leaks, replace the faulty hoses, tighten loose clamps, or repair/replace the radiator as needed. After repairs, refill the system with the correct John Deere COOL-GARD II coolant.

2. 2

   Replace the radiator cap

   If the radiator cap failed the pressure test, replace it with a new OEM part matching the correct pressure rating for the specific machine.

3. 3

   Replace the coolant pressure sensor

   If all other diagnostic steps have been exhausted and the system is confirmed to be mechanically sound, replace the coolant pressure sensor. Disconnect the electrical connector, carefully unscrew the old sensor, install the new sensor to the correct torque specification, reconnect the wiring, and top off the coolant.