Case IH 3529 (F-3232-05) – Engine Control Unit (ECU): Downstream NOx sensor internal failure (Heater Open Circuit Error)

Nitrogen Oxide (NOx) sensors contain an internal heating element that brings the sensor up to its required operating temperature to accurately measure exhaust gases. An 'Open Circuit' or 'Open Load' error means the electrical path for this heater has been broken. Because the code specifies an internal failure, it almost always indicates that the heating element inside the sensor itself has burned out or a wire inside the sensor housing has severed.

• VESTRUM CVX
• Case IH 240 Series Axial-Flow Combines
• Case IH Magnum 235 – 340 (Series 4)
• Case IH Steiger series
• Case IH Farmall series

1. 1

   Inspect the wiring harness and the connector leading to the downstream NOx sensor for melted wires, chafing against the exhaust, or corrosion inside the connector pins.

2. 2

   Verify that the ECU is sending the proper voltage and ground to the sensor's heater circuit pins on the machine-side of the harness.

3. 3

   Confirm internal failure: if the harness is supplying power and ground correctly but the code persists, the open load is an internal break inside the sensor.

1. 1

   Cool Down

   Ensure the machine is turned off and the exhaust system has completely cooled to prevent severe burns.

2. 2

   Locate the Sensor

   Locate the downstream NOx sensor. It is mounted in the exhaust pipe directly after the SCR (Selective Catalytic Reduction) catalyst / tailpipe.

3. 3

   Disconnect

   Unplug the sensor's electrical connector from the main engine wiring harness.

4. 4

   Remove the Sensor

   Use a specialized NOx/O2 sensor socket or a wrench to unscrew the sensor from the exhaust pipe. (Note: Penetrating oil may be required, as exhaust sensors frequently seize in the bung).

5. 5

   Install the New Sensor

   Apply a small amount of high-temp anti-seize compound to the threads of the new sensor (if it does not come pre-applied). Be extremely careful not to get any anti-seize on the sensor probe tip, as this will ruin it. Thread it in and tighten to OEM torque specifications.

6. 6

   Reconnect

   Plug the new sensor's electrical connector back into the harness.

7. 7

   Clear Codes

   Connect the Case IH Electronic Service Tool (EST) or a compatible diagnostic scanner to clear the inactive 3529 fault code.

8. 8

   Test Run

   Run the machine to allow the exhaust to heat up. The ECU will run a self-diagnostic on the heater circuit to confirm the repair.