Case IH 3687 (DTC 3E1C) - ECU – Engine Control Unit (ECU / ECM): SCR upstream temperature sensor signal drift at cold start

The control module has detected that the temperature reading from the Selective Catalytic Reduction (SCR) upstream temperature sensor is drifting or implausible when compared to other temperature sensors (such as ambient air or engine coolant) during a cold start (after a cold soak). This typically indicates a failing sensor element whose calibration has drifted, or excessive resistance in the sensor's wiring circuit.

• MAXXUM T4E
• Case IH 240 Series Axial-Flow Combines
• Case IH Steiger Tractors (e.g., 620)
• Case IH Magnum CVT/CVX Tractors (e.g., 265)
• Case IH Farmall and Maxxum Tractors
• Case IH / Austoft Harvesters (e.g., 9900)

1. 1

   Perform a cold soak comparison: Allow the machine to sit overnight so the engine and exhaust are completely cold. Use a scan tool to compare the SCR upstream temperature sensor reading to ambient air, engine coolant, and DOC/SCR downstream temperature sensors. If it reads significantly higher or lower, the sensor is faulty.

2. 2

   Inspect the wiring harness leading to the SCR upstream temperature sensor for chafing, melting from exhaust heat, or breaks.

3. 3

   Disconnect the sensor connector (C191) and inspect the 2-wire female connector and 4mm terminals for corrosion, moisture, or loose pins that can cause false resistance and signal drift.

1. 1

   Turn off the machine, remove the key, and disconnect the battery to prevent electrical shorts.

2. 2

   Locate the SCR upstream temperature sensor.

   It is threaded into the exhaust pipe after the Diesel Oxidation Catalyst (DOC) and dosing module, but before the main SCR catalyst.

3. 3

   Disconnect the electrical connector from the sensor pigtail.

4. 4

   Using a suitable wrench or sensor socket, carefully unscrew the faulty temperature sensor from the exhaust pipe.

   Penetrating oil may be required if the sensor is seized from exhaust heat.

5. 5

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

   If not already pre-applied by the manufacturer. Do not get anti-seize on the sensor probe.

6. 6

   Thread the new SCR upstream temperature sensor into the exhaust pipe and tighten to the OEM torque specification.

7. 7

   Reconnect the electrical connector, ensuring it clicks into place securely.

8. 8

   Reconnect the battery.

9. 9

   Connect a diagnostic scan tool to the machine and clear the 3687 (3E1C) fault code from the Engine ECU.

10. 10

    Start the engine and monitor the live data to ensure the temperature sensor is reading correctly and the code does not return.