John Deere 1538 – HCU: Reel Height Sensor Voltage Too High

The Reel Height Sensor is reporting a voltage to the Header Control Unit (HCU) that exceeds the normal operating range, specifically reading greater than 4.5 VDC. The standard operating voltage for this sensor is between 0.5 and 4.5 volts. A voltage reading above this threshold indicates a potential electrical fault in the sensor's circuit, which is typically caused by a faulty sensor, a short to a power source, or an issue within the wiring harness.

• 9450
• 9550
• 9650
• 9560 STS
• 9660 STS
• 9760 STS
• 9670 STS
• 9770 STS
• S-Series Combines
• S550
• S660
• S670
• S680
• S690
• 70 Series Combines
• Combines equipped with 600FD-Flexible Draper Platforms

1. 1

   Visually inspect the Reel Height Sensor and its wiring harness for frayed or pinched wires, corrosion on connectors, or damage to the sensor body, paying close attention to areas where the harness flexes.

2. 2

   Access the onboard diagnostic system through the cab display (navigate to HCU or LC1) to view the live voltage reading from the Reel Height Sensor. The voltage should typically be between 0.5 and 4.5 volts (low around 1.0-1.5V when fully lowered, high around 3.0-4.2V when fully raised). A consistently high reading, regardless of reel position, points to a fault.

3. 3

   Attempt to run the header calibration procedure as outlined in the operator's manual. A failed calibration often indicates an issue with one of the header sensors.

1. 1

   Isolate the fault (Sensor vs. Wiring)

   Disconnect the wiring harness from the Reel Height Sensor. Using a multimeter, check for a 5-volt reference signal and a good ground connection at the sensor connector on the harness side. Inspect the wiring for a short to a power source, which could be caused by rodent damage or chafing.

2. 2

   Diagnose HCU/Wiring vs. Sensor

   If the 5-volt reference is missing or the ground is faulty, the issue lies within the wiring harness or the HCU. If both are present and the wiring is not shorted to power, the sensor is the most likely cause of the problem.

3. 3

   Replace the Reel Height Sensor

   If the sensor is determined to be faulty, disconnect the electrical connector and unbolt the sensor from its mounting bracket. Install the new sensor, ensuring the sensor arm is correctly oriented for the specific combine brand, and reconnect the harness.

4. 4

   Perform post-repair calibration

   Clear the fault code from the diagnostic system. Perform a header calibration to ensure the new sensor is properly integrated. Operate the reel height adjustment and monitor the sensor voltage in the diagnostic menu to confirm it reads correctly (low around 1.0-1.5V when fully lowered, high around 3.0-4.2V when fully raised).