John Deere 000110.04 – ECU, CCU, or A00: Engine Coolant Temp Sensor Signal Voltage Low

The Engine Control Unit (ECU) has detected that the voltage signal from the engine coolant temperature sensor is below the normal operating range, indicating a potential short circuit or sensor failure. The ECU relies on this signal to optimize fuel delivery, control ignition timing, and manage the cooling fan. An incorrect signal can cause difficult cold starts, rough idling, poor fuel economy, inaccurate dashboard temperature readings, and may force the engine into a derated or limp mode to prevent perceived overheating.

• 5045E
• 5055E
• 5065E
• 5075E
• 5065M
• 5075M
• 5085M
• 5090M
• 5095M
• 5095MH
• 5100M
• 5105M
• 5115M
• 6E Series
• 6M Series
• 9R Series
• 9RT Series
• 9RX Series
• 9650 STS
• 9750 STS
• 4.5L PowerTech Engine
• 6.8L PowerTech Engine
• 6B Series
• 6R Series
• 4045 Engine
• 6068 Engine

1. 1

   Visually inspect the Engine Coolant Temperature sensor's electrical connector and surrounding wiring harness for corrosion, bent terminals, cracked or frayed wires, or coolant contamination.

2. 2

   Check for a 5-volt reference voltage at the sensor's electrical connector with the key in the 'ON' position and the sensor unplugged. Absence of voltage indicates a wiring or ECU issue.

3. 3

   Test the sensor's internal resistance using a multimeter set to ohms (Ω) with the sensor disconnected. A reading of zero ohms indicates a shorted sensor, while 'OL' indicates an open circuit. General values are around 2,500 Ω at 20°C (68°F) and 300 Ω at 80°C (176°F). Typical John Deere values are approximately 153.9 Ω at 122°F and 51.9 Ω at 176°F.

1. 1

   Prepare machine

   Ensure the engine is cool to prevent burns. Park the machine on a level surface and engage the parking brake.

2. 2

   Locate and prep sensor area

   Locate the ECT sensor on the engine block, typically near the thermostat housing (e.g., on the driver's side behind the A/C compressor on the 5100E). Partially drain the cooling system into a clean container to prevent coolant loss.

3. 3

   Disconnect sensor

   Disengage the locking tab (often a small red tab) on the electrical connector and unplug it from the sensor.

4. 4

   Remove old sensor

   Using an appropriate deep socket (e.g., 7/8-inch), carefully loosen and remove the faulty sensor.

5. 5

   Install new sensor

   Thread the new sensor in by hand to avoid cross-threading, then tighten to the manufacturer's specified torque. Most new sensors include a pre-installed O-ring.

6. 6

   Reconnect and refill

   Firmly push the electrical connector onto the new sensor until it clicks, re-engage the locking tab, and top off the cooling system with coolant.

7. 7

   Test and clear codes

   Start the engine, allow it to reach operating temperature, and check for leaks. Use a diagnostic tool to clear the fault code and verify it does not return.