Case IH 3686 (DTC 3D1C) - ECU – Engine Control Module (ECM) / Engine Control Unit (ECU): DOC upstream temperature sensor signal drift at cold start

The control module has detected that the temperature reading from the sensor located just before the Diesel Oxidation Catalyst (DOC) is not plausible during a cold engine start. The reading drifts or deviates significantly from the expected baseline cold temperature compared to other temperature sensors.

• MAXXUM T4E
• 240 Series Axial-Flow Combines
• Steiger
• Magnum
• Maxxum
• Farmall
• Case N-Series Loader Backhoes

1. 1

   Check for related active faults, specifically DTC-352C (SPN-13612) for 'Upstream oxidation catalyst temperature sensor comparison', and diagnose those first if active.

2. 2

   Verify the upstream oxidation catalyst temperature sensor is physically installed correctly and securely in the exhaust pipe.

3. 3

   Visually inspect the sensor's wiring harness and connector (C189 or X189) for damage, bent or dislocated pins, corroded terminals, or broken wires, and ensure the connector is fully seated.

4. 4

   Perform a harness flex test by flexing the involved harnesses while monitoring the diagnostic display to reveal any intermittent breaks or shorts in the wiring.

5. 5

   Perform resistance testing on the sensor using a multimeter to check the cold resistance and ensure it is not completely open or shorted.

1. 1

   Safety First

   Ensure the machine is parked safely, the engine is turned off, and the exhaust system has completely cooled down to avoid severe burns.

2. 2

   Disconnect the Harness

   Locate the DOC upstream temperature sensor (Exhaust Gas Temperature Sensor 1) in the exhaust piping before the DOC canister. Disconnect the 2-wire electrical connector.

3. 3

   Remove the Sensor

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

4. 4

   Install the New Sensor

   Thread the new DOC upstream temperature sensor into the exhaust pipe. Tighten it to the OEM torque specification (do not overtighten, as these sensors are fragile).

5. 5

   Reconnect Wiring

   Reconnect the electrical harness, ensuring the locking tab on the connector clicks into place. If the connector itself was damaged, splice in a new connector/terminal kit.

6. 6

   Clear Codes and Verify

   Use the Case IH Electronic Service Tool (EST) or DATAR to clear the fault codes. Start the engine and allow it to reach operating temperature, or perform a manual/service regeneration to verify the sensor is reading correctly and the code does not return.