John Deere 172 – ACU: Outside Air Temp Sensor Voltage High

The CLIMATRAK Outside Air Temperature Sensor is reporting a voltage to the control unit that is too high (exceeding 4.8 VDC). This indicates that the sensor resistance is greater than 60KΩ, which the system interprets as an extremely cold temperature of -22°F or -30°C.

• 9540
• 9560
• 9580
• 9640
• 9660
• 9680 WTS
• 9650 STS
• 9750 STS
• 9660 CTS
• 3032e
• 3038
• 8420
• 9230
• 9330
• 9430
• 9530
• 9630
• 9560 STS
• 9570 STS
• 9660 STS
• 9660 WTS
• 9670 STS
• 9760 STS
• 9770 STS

1. 1

   Visually inspect the wiring harness and connector for the outside air temperature sensor (typically located behind the front grill or bumper near the cab air inlet) for chewed or frayed wires.

2. 2

   Ensure the sensor connector is clean, free of corrosion, and securely fastened.

3. 3

   Check the circuit for an open condition, which is a common cause for a high voltage reading.

4. 4

   Perform a multimeter test on the disconnected sensor to measure resistance (Ohms); an open circuit (no reading) indicates a failed sensor.

5. 5

   Warm the sensor with a heat gun or hairdryer while measuring resistance; if the resistance value remains static instead of changing, the sensor is defective.

1. 1

   Safety First

   Park the machine on a level surface, turn off the engine, and remove the key.

2. 2

   Locate the Sensor

   Find the ambient or outside air temperature sensor, generally positioned at the front of the vehicle near the cab's fresh air intake.

3. 3

   Inspect Wiring

   Repair any damaged wires found during the visual inspection and clean any corrosion from the connector.

4. 4

   Test the Sensor

   If the wiring appears to be in good condition, test the sensor with a multimeter as described above.

5. 5

   Replace the Sensor

   If the sensor fails the multimeter test, it must be replaced. Disconnect the electrical connector, remove any mounting hardware, and install the new sensor.

6. 6

   Clear Codes

   After the repair is complete, reconnect the battery if it was disconnected, start the machine, and use the diagnostic display or a service tool to clear the fault code.

7. 7

   Verify Operation

   Operate the CLIMATRAK system and check the outside temperature reading on the display to ensure it is providing a plausible value.