Case IH F-3216-31 - ECU – Engine Control Unit (ECU): Upstream NOx sensor supply voltage is out of range

The system has detected that the electrical supply voltage to the Upstream NOx sensor (the sensor located in the exhaust stream before the Diesel Oxidation Catalyst / SCR assembly) is outside of normal operating parameters. This typically points to a short to ground, a short to battery power, an open circuit in the wiring harness, or an internal failure of the sensor's own control module.

• MAGNUM AFS Connect
• Magnum (180-380)
• Steiger (370-620)
• Puma (150-220)
• Maxxum (115-150)
• Farmall series
• Axial-Flow Combines (e.g., 240 Series)
• Austoft series sugarcane harvesters (e.g., 9900)

1. 1

   System Voltage Check: Verify the machine's battery voltage and alternator output. Low system voltage during cold starts or a failing alternator can trigger false voltage out-of-range codes.

2. 2

   Visual Inspection: Locate the Upstream NOx sensor (before the DOC/SCR) and trace its wiring harness back to the ECU. Look for melted wires, chafing against the chassis, or breaks.

3. 3

   Connector Check: Disconnect the NOx sensor. Inspect the pins for corrosion, moisture/water ingress, or pushed-back pins.

4. 4

   Circuit Testing: Using a multimeter, turn the key to the ON position and probe the harness side of the connector to ensure it is receiving the correct supply voltage (typically 12V or 24V depending on the machine) and has a solid ground. If voltage is missing, check the aftertreatment system fuses and relays.

1. 1

   Power Down

   Turn off the engine, remove the key, and disconnect the machine's battery to prevent electrical spikes.

2. 2

   Locate the Sensor

   Identify the Upstream NOx sensor in the exhaust pipe, located between the engine turbocharger and the DOC/SCR catalyst assembly.

3. 3

   Disconnect

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

4. 4

   Remove the Sensor

   Using a specialized NOx/O2 sensor socket (usually 22mm), carefully unscrew the sensor probe from the exhaust pipe. Note: If the sensor is seized due to heat cycling, apply penetrating oil and allow it to soak before applying torque to avoid stripping the exhaust bung threads.

5. 5

   Install the New Sensor

   Apply a small amount of anti-seize compound to the threads of the new sensor (if not pre-applied) and thread it into the exhaust pipe. Torque to the manufacturer's specification.

6. 6

   Route Wiring

   Reconnect the electrical plug to the harness. Ensure the wiring is secured with zip-ties or clips, keeping it safely away from extreme exhaust heat sources.

7. 7

   Relearn/Clear Codes

   Reconnect the battery. Connect the Case IH Electronic Service Tool (EST) to clear the F-3216-31 fault code. Run the engine and perform an aftertreatment system diagnostic test to verify the new sensor is reading correctly and the code does not return.