John Deere 001548.04 – ATC or ETC: Low Voltage On Vent Outlet Air Temp Sensor

The controller has detected that the signal voltage from the vent outlet air temperature sensor (Sending Unit B128) has dropped below 0.1 VDC (or below 0 volts). This condition typically means that the sensor's internal resistance has dropped below 50 Ohms (which the system interprets as an impossibly high temperature of 293°F / 145°C), or there is a direct short to ground in the sensor's wiring circuit. When this code is active, the controller restricts automatic temperature control, and the water valve is adjusted based only on the difference between the actual cab temperature and the desired temperature.

• 6110R
• 6120R
• 6130R
• 6145R
• 6155R
• 6175R
• 6195R
• 6215R (2015-2021)
• 6230
• 6330
• 6430
• 7130 to 7530 Premium
• 7715
• 7720
• 7815
• 7820
• 7920
• 8130
• 8230
• 8330
• 8430
• 8530
• 8230T
• 8330T
• 8430T
• 8310RT
• 8335RT
• 8360RT
• 9430
• 9530
• 9630

1. 1

   Restart the tractor to verify if the fault code clears, as it may be an intermittent communication error

2. 2

   Inspect the cab recirculation air filter to ensure it is clean and not plugged

3. 3

   Inspect the air conditioning condenser at the front of the tractor to ensure it is clean

4. 4

   Visually inspect the wiring harness leading to the vent outlet air temperature sensor (Component B128) for signs of damage, chafing, or corrosion that could cause a short to ground

1. 1

   Gain access to sensor

   Locate the vent outlet air temperature sensor (B128) within the cab's HVAC system. This will likely require removing panels in the cab roof area.

2. 2

   Test sensor circuit

   Test the sensor's electrical circuit for a short to ground by checking for continuity to ground on the signal wire.

3. 3

   Test sensor resistance

   Test the sensor itself to ensure it is functioning within its specified resistance range.

4. 4

   Replace component

   If the sensor tests out of specification or the wiring is damaged beyond repair, replace the faulty component.