Case IH 3533 (F-518867-09) – Engine Control Unit (ECU) / Engine Management System (EMS): CAN timeout error from downstream NOx sensor

The engine's control system has lost communication with the downstream NOx sensor over the CAN bus network. The sensor is located directly after the Selective Catalytic Reduction (SCR) catalyst and measures the pollutants exiting the tailpipe. When the module stops receiving data from this sensor, it triggers the 3533 code and will eventually induce engine torque limitation (derate) to protect the SCR system.

• VESTRUM CVX
• Magnum Series (180–380)
• Steiger & Quadtrac (350–620)
• Puma (150–220)
• Maxxum (115–150)
• Farmall (110A–140A, 40-50)
• Axial-Flow 240 Series
• 5130
• 6130
• 7130
• 8230
• 9230
• Titan 2240
• 3030
• 3530
• 4030
• 4530
• Case Wheel Loaders (521F through 1121F)

1. 1

   Check Power and Ground: Verify the machine voltage. The AdBlue tank and both NOx sensors share the same power source and relay. A failure here will drop communication to the sensor.

2. 2

   Inspect Connectors: Check for damaged or loose machine grounds and connector pins. Look closely for debris or water intrusion inside the connector terminals, which is a common consequence of pressure washing the engine or poor connector sealing.

3. 3

   Inspect the Harness: Ensure the wiring harness is not chafed, melted, or damaged, and verify it is routed correctly away from extreme exhaust heat.

1. 1

   Safety First

   Stop the engine and let the exhaust system cool completely before starting work. Do not start the engine during the service procedures.

2. 2

   Clean and Secure Connections

   If water or debris is found in the downstream NOx sensor connector, clean the terminals with electrical contact cleaner, dry thoroughly, and apply dielectric grease. Reconnect and ensure the locking tab is secure.

3. 3

   Repair Wiring

   If the harness is damaged or a ground is loose, repair the wiring fault and re-test the CAN network.

4. 4

   Replace the Sensor

   If the wiring, power, and ground are all verified to be in good working order, the downstream NOx sensor has failed internally and must be replaced.

5. 5

   Clear Codes

   After fitting the new NOx sensor, connect a diagnostic tool to clear the error codes. The system may require a warm-up cycle to reach the "Dew Point" before the new sensor reads as "Ready".