Case IH F-3232-12 - ECU – Engine ECU: Downstream NOx sensor internal failure (Heater Performance Plausibility Error)

The internal heating element of the downstream Nitrogen Oxide (NOx) sensor is not functioning as expected. The control module is seeing a voltage, current draw, or temperature rise from the heater circuit that does not make logical sense.

• MAGNUM AFS Connect
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Magnum series
• Steiger series
• Farmall series (110A-140A, CVT models)
• Austoft 9900 sugarcane harvesters

1. 1

   Check system voltage at the battery and alternator, as low voltage or high resistance during a cold start can trigger heater plausibility errors.

2. 2

   Inspect the downstream NOx sensor wiring harness and connector for chafed wires, melted insulation, or pushed-out pins.

3. 3

   Perform a CAN communication test to verify the sensor is receiving proper power, ground, and CAN Hi/CAN Lo signals from the ECU.

4. 4

   Inspect the exhaust system for leaks near the downstream sensor (located after the SCR catalyst), which can skew heater plausibility logic.

1. 1

   Power Down

   Turn off the machine and disconnect the battery to prevent electrical spikes.

2. 2

   Locate the Sensor

   Locate the downstream NOx sensor on the exhaust tailpipe, positioned after the SCR/DPF catalyst assembly.

3. 3

   Disconnect

   Unplug the electrical connector from the sensor's control module box. Unbolt the module box from its mounting bracket.

4. 4

   Remove Sensor

   Using a specialized NOx/O2 sensor socket (usually 22mm), carefully unscrew the sensor probe from the exhaust pipe.

5. 5

   Prep the New Sensor

   Apply a small amount of high-temperature anti-seize compound to the threads of the new sensor (if it does not come pre-applied). Caution: Do not get any anti-seize on the sensor tip, as this will ruin the element.

6. 6

   Install

   Thread the new sensor into the exhaust pipe and torque to OEM specifications (typically 50 ± 10 Nm).

7. 7

   Route Wiring

   Mount the sensor's control box to the bracket. Route the cable carefully, ensuring it is secured at least 100mm away from the control unit to prevent vibration damage, and keep it clear of direct heat sources. Reconnect the electrical plug.

8. 8

   Clear Codes

   Reconnect the battery. Use a diagnostic service tool (like the Case IH EST) to clear the inactive F-3232-12 fault code. Run the engine through a warmup cycle to verify the code does not return.