John Deere 109.03 – ECU: Engine Coolant Pressure Signal Out of Range High

The signal voltage returning from the coolant pressure sensor to the control module is higher than the maximum allowed threshold. This usually points to a short circuit to a 12-volt power source in the sensor wiring harness, a loss of the sensor ground, or an internally shorted/failed coolant pressure sensor.

• 6110M
• 6120M
• 6130M
• 6145M
• 6155M
• 6175M
• 6195M
• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 7200R
• 7215R
• 7230R
• 7250R
• 7270R
• 7280R
• 7290R
• 7310R
• 8235R to 8400R
• 8310RT
• 8335RT
• 8360RT
• 9360R to 9640R
• 9470RT
• 9520RT
• 9570RT
• S650
• S660
• S670
• S680
• S690
• S760
• S770
• S780
• S790
• T-Series
• W-Series
• X9 Series
• 7180
• 7280
• 7380
• 7480
• 7580
• 7780
• 7980
• 8000 Series
• 9000 Series
• R4038
• R4044
• R4040I
• R4050I
• 408R
• 410R
• 412R
• 250D

1. 1

   Visually inspect the coolant pressure sensor, 3-pin connector, and wiring harness leading to the ECU for chafing, melted insulation, or exposed wires that could cause a short to 12V.

2. 2

   Disconnect the sensor and check for water intrusion, corrosion, or bent pins inside the connector, which can bridge the 12V reference/supply wire to the signal wire.

3. 3

   Perform a voltage test with the key in the ON position (engine off): probe the sensor harness connector to verify the 5V reference voltage, check the signal wire for an abnormal 12V presence (confirming a short to power), and check the ground pin for high resistance.

4. 4

   If wiring tests perfectly normal (no shorts to power, good ground, proper reference voltage), the internal circuitry of the sensor has likely failed and is outputting a high voltage.

1. 1

   Turn off the machine, remove the key, and allow the engine and coolant to cool down completely to avoid burn hazards and system pressure.

   Cool down engine and coolant.

2. 2

   Relieve any residual pressure in the cooling system by slowly loosening the coolant reservoir cap.

   Relieve cooling system pressure.

3. 3

   Locate the coolant pressure sensor. Disconnect the 3-pin electrical connector.

   Disconnect sensor connector.

4. 4

   If the diagnostic checks revealed a wiring short to 12V, repair the damaged section of the harness or splice in a new pigtail connector.

   Repair wiring short to 12V if found.

5. 5

   If the sensor is faulty, use a wrench to unthread the old sensor (Thread fitting OD: 11.8mm). Have a rag ready to catch any minor coolant spillage.

   Remove faulty sensor.

6. 6

   Thread the new coolant pressure sensor into the port and tighten to OEM specifications.

   Install new sensor.

7. 7

   Reconnect the 3-pin electrical connector, ensuring it clicks securely into place.

   Reconnect sensor connector.

8. 8

   Top off the engine coolant if any was lost during the swap.

   Top off coolant.

9. 9

   Turn the key on and use a diagnostic tool to clear the 000109.03 ECU fault code.

   Clear fault code.

10. 10

    Start the engine, check for coolant leaks around the new sensor, and verify that the code does not return.

    Verify repair and check for leaks.