Case IH F-4766-02 - ECU – Engine Control Unit (ECU): SCR upstream temperature sensor signal drift at cold start

This condition indicates a plausibility error. The engine control system runs a check when the machine is completely cooled down to ambient temperature (a "cold start"). During this check, the SCR (Selective Catalytic Reduction) upstream temperature sensor is compared against other temperature sensors (such as the intake humidity/temperature sensor and the SCR downstream temperature sensor). If the SCR upstream sensor's reading drifts or does not match the ambient temperature baseline established by the other sensors, this fault is triggered.

• MAGNUM AFS Connect
• Magnum 200 AFS Connect
• Magnum 340 AFS Connect
• Magnum 400 AFS Connect
• Axial-Flow 240 Series
• Axial-Flow 6130
• Axial-Flow 6140
• Axial-Flow 8230
• Axial-Flow 8250
• Maxxum 115
• Maxxum 125
• Maxxum 135
• Maxxum 145
• Maxxum 150
• Farmall 105 A
• Quadtrac 470

1. 1

   Cold Engine Sensor Verification: Allow the engine to cool completely to ambient temperature. Using a diagnostic service tool, monitor the live data for the intake humidity/temperature sensor, the DOC upstream temperature sensor, the SCR upstream temperature sensor, and the SCR downstream temperature sensor. All of these sensors should read approximately the same ambient temperature.

2. 2

   Wiring and Connector Inspection: The SCR upstream temperature sensor utilizes a 2-way Bosch BDK 2.8 connector. Inspect the wiring harness, the female connector, and the terminals (4mm) for corrosion, moisture intrusion, or damaged pins that could cause excess resistance and skew the temperature signal.

3. 3

   Check for Related Codes: Verify if there are active codes for the intake humidity/temperature sensor or other exhaust sensors, as a failure in the baseline reference sensor can falsely trigger a plausibility fault for the SCR sensor.

1. 1

   Ensure the machine is turned off, the battery disconnect is switched off, and the exhaust system has completely cooled to avoid severe burns.

2. 2

   Locate the SCR upstream temperature sensor.

   According to the FPT engine service manual, it is physically located in the exhaust stream after the Diesel Oxidation Catalyst (DOC) / DEF Mixer and directly before the Selective Catalytic Reduction (SCR) catalyst.

3. 3

   Disconnect the 2-wire Bosch BDK 2.8 electrical connector from the sensor harness.

4. 4

   Carefully unscrew the faulty temperature sensor from the exhaust pipe bung.

5. 5

   Install the new SCR upstream temperature sensor.

   If the new sensor does not have pre-applied anti-seize, apply a small amount of high-temp sensor-safe anti-seize to the threads, ensuring none gets on the probe itself.

6. 6

   Reconnect the electrical connector, ensuring the locking tab clicks into place.

7. 7

   Power on the machine, connect the diagnostic tool, and clear the ECU fault codes.

8. 8

   Perform a cold start and verify via live data that the sensor reading is now plausible and tracks correctly as the exhaust heats up.