John Deere 170.04 – ATC: Inside Air Temperature Sensor Voltage Too Low

The controller measures below 0 volts (or less than 0.1 VDC) at the signal input of the inside air temperature sending unit (sensor B127). This indicates a short to ground in the circuit, or that the sensor's internal resistance has dropped below 50-52 ohms. Automatic temperature control is restricted, and the system may default to using the actual outlet air temperature sensor instead.

• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 6000 series
• 6120-6420
• 7000 series
• 7720-7920
• 8000 series
• 8130-8530
• 9000 series
• 9330-9630
• R/RT series
• STS series
• WTS series
• 9450
• 9550
• 9650 STS
• 9750 STS
• Sprayers
• Forage Harvesters

1. 1

   Locate Sensor B127 (inside air temperature sensor), often located behind the training seat or in the cab roof/duct area.

2. 2

   Inspect the wiring harness (specifically lead 2007) and the sensor connector for damaged insulation, pinched wires, or corrosion that could cause a short to ground.

3. 3

   Use a multimeter to measure the voltage at the sensor's input. A reading consistently below 0.1 VDC confirms a short to ground.

4. 4

   Disconnect the sensor and measure its resistance. If the resistance is less than 50 ohms, the sensor is internally shorted and defective.

1. 1

   Turn off power

   Turn off the machine's engine and electrical power.

2. 2

   Access sensor

   Access the B127 Cab Temperature Sensor. Ensure it is not covered by debris or aftermarket cab accessories, which can sometimes cause erratic readings.

3. 3

   Disconnect harness

   Disconnect the wiring harness from the sensor.

4. 4

   Remove sensor

   If the diagnostic tests proved the wiring is intact but the sensor is shorted, remove the faulty sensor from its mounting bracket.

5. 5

   Install new sensor

   Install the new OEM replacement sensor and securely reconnect the wiring harness.

6. 6

   Clear codes

   Turn the machine's power back on and clear the stored ATC codes via the CommandCenter or diagnostic switch.

7. 7

   Verify repair

   Run the HVAC system in 'AUTO' mode to verify that the cab temperature regulates correctly and the code does not return.