John Deere 109.04 – Engine Control Unit (ECU): Engine Coolant Pressure Signal Out of Range Low

The coolant pressure sensor signal voltage has dropped below the acceptable threshold. This is typically caused by a short circuit to ground in the 12V sensor wiring, or an actual severe drop in engine coolant pressure. Engine power is often limited by the system to prevent damage.

• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 8245R
• 8400R
• 8310RT
• 8335RT
• 8360RT
• 7180
• 7280
• 7380
• 7480
• 7580
• 7780
• 7980
• S-Series Combines
• R-Series Sprayers

1. 1

   Check the physical engine coolant level to ensure it is not critically low

2. 2

   Inspect the cooling system for any visible external leaks

3. 3

   Inspect the sealed lid (radiator cap) and the sealing components of the cooling system to ensure they are holding pressure

4. 4

   Test the coolant pressure sensor wiring harness for a short circuit to ground

1. 1

   Fill coolant and pressure test

   If the coolant level is low, fill the coolant to the appropriate level and pressure test the system to locate and repair any leaks.

2. 2

   Clean or replace radiator cap

   If the radiator cap (sealed lid) is faulty or failing to hold pressure, clean the sealing surfaces or replace the cap.

3. 3

   Inspect and repair wiring

   If the physical pressure is fine but the code persists, trace the wiring from the ECU to the coolant pressure sensor. Repair any frayed wires or shorts to ground.

4. 4

   Replace coolant pressure sensor

   If the wiring is intact and the system holds pressure, the coolant pressure sensor itself has likely failed and must be replaced.