Case IH 3687 (F-4766-02) – Engine Control Module (ECM / ECU): SCR upstream temperature sensor signal drift at cold start

The Engine Control Module (ECM) has detected that the temperature sensor located just before the Selective Catalytic Reduction (SCR) catalyst is reporting a value that deviates significantly from the expected ambient temperature (or from the readings of other temperature sensors) during a cold start.

• VESTRUM CVX
• 240 Series Axial-Flow (6140, 7140, 8240, 9240, AFX 6130, AF 8250, AFX 9250)
• Quadtrac series (580)
• Farmall series (40-45-50 CVT, 115 U)
• Maxxum series (115, 125, 135, 145, 150)
• Luxxum 100
• Quantum 90CL
• Austoft 9000 series

1. 1

   Environmental Check: Verify if an external heat source (such as parking the tractor's exhaust near a building's HVAC exhaust vent) artificially heated the sensor's environment. If so, clear the code and park the machine in a neutral environment.

2. 2

   Live Data Verification: Connect a diagnostic scan tool and monitor the exhaust temperature sensors (DOC upstream, SCR upstream, and SCR downstream) when the engine is completely cold. All sensors should read roughly the same ambient temperature.

3. 3

   Wiring and Connector Inspection: Inspect the 2-wire connector (C191) for the SCR upstream temperature sensor for corrosion, pushed-out pins, or wire chafing.

1. 1

   Ensure the machine is turned off and the exhaust system is completely cool to avoid severe burns.

   Safety precaution before beginning work.

2. 2

   Locate the SCR upstream temperature sensor.

   It is threaded into the exhaust pipe just before the SCR catalyst (after the DOC/Mixer).

3. 3

   Disconnect the 2-wire electrical connector (C191) from the sensor.

   Prepare the sensor for removal.

4. 4

   Using an appropriate sensor socket or wrench, carefully unthread the faulty temperature sensor from the exhaust pipe.

   Remove the faulty sensor.

5. 5

   Apply a small amount of high-temperature anti-seize compound to the threads of the new sensor.

   Only apply if it does not come pre-applied from the factory. Ensure no anti-seize gets on the sensor probe itself.

6. 6

   Thread the new sensor into the exhaust pipe and tighten it to the OEM torque specification.

   Install the replacement sensor.

7. 7

   Reconnect the electrical connector.

   Ensure the locking tab clicks securely into place.

8. 8

   Turn the key to the ON position and use a diagnostic scan tool to clear the fault codes.

   Clear the ECM memory of the old fault.

9. 9

   Start the engine and monitor the live sensor data.

   Ensure it is reading correctly and the fault does not return.