John Deere 524202.04 – ATC (Automatic Temperature Control / Air Conditioning Module): B126 Sensor for Ambient Air Temperature (at Rear), Voltage Too Low

Triggered when the control unit measures 0 volts at the signal input for the ambient air temperature sensor (B126, lead 2006). This typically indicates the sensor's circuit is shorted to ground or the sensor has failed internally. The climate control system restricts temperature control and defaults to using the front ambient temperature sensor (B125).

• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R
• 8225R through 8400R
• 8310RT through 8360RT
• 9470RT
• 9520RT
• 9570RT
• 6230
• 6330
• 6430
• 6020 to 6920S

1. 1

   Access onboard diagnostics via the tractor's display or John Deere Service Advisor.

2. 2

   Check sensor data at diagnostic address ATC014 (or ATC902) for the rear ambient sensor temperature. A normal reading is between -40.0 °C and 65 °C. An 'Err' reading indicates a faulty circuit.

3. 3

   Check signal voltage at diagnostic address ATC043. A normal operating voltage is between 0.0 and 5.0 volts. A reading of exactly 0.0V confirms a short to ground.

4. 4

   Disconnect the B126 ambient air temperature sensor located in the cab roof to isolate the short.

5. 5

   If the 5V reference voltage returns at the harness connector when unplugged (sensor cause): the sensor is internally shorted and must be replaced.

6. 6

   If the voltage remains at 0V with the sensor unplugged (wiring cause): the wiring harness (lead 2006) is shorted to ground. Inspect for chafing, pinched wires, or corrosion.

1. 1

   Power Down

   Turn off the ignition and disconnect the battery to prevent electrical spikes during repair.

2. 2

   Access the Sensor

   Locate the B126 ambient air temperature sensor. Depending on the exact cab configuration, it is located in the cab roof (either at the rear or above the right-side front corner).

3. 3

   Repair Wiring (Wiring cause)

   If the diagnostic checks pointed to a harness issue, trace lead 2006 back to the ATC module. Repair or splice any damaged, bare, or pinched wires that are grounding out against the cab frame.

4. 4

   Replace the Sensor (Sensor cause)

   If the sensor is internally shorted, unclip the faulty sensor from its mounting bracket, plug the new OEM sensor into the harness, and secure it in place.

5. 5

   Clear Codes

   Reconnect the battery and turn the ignition ON. Use the John Deere Service Advisor or the onboard diagnostic menu to clear the stored ATC 524202.04 fault code.

6. 6

   Verify Operation

   Return to diagnostic address ATC043 to ensure the signal voltage is now fluctuating normally between 0.0V and 5.0V, and verify the climate control system operates correctly.