Case IH 3686 (F-4765-14) – Engine Control Module (ECM / Engine ECU): DOC upstream temperature sensor signal drift at cold start.

This fault indicates that the temperature sensor located just before (upstream of) the Diesel Oxidation Catalyst (DOC) is reporting an implausible temperature reading when the engine is started cold. The Engine Control Module (ECM) compares the exhaust temperature sensors to ambient air and engine coolant temperatures after a long "cold soak." If the DOC upstream sensor's reading drifts significantly out of range compared to the other sensors, this code is triggered.

• VESTRUM CVX
• 240 Series Axial-Flow Combines (7240, 8260, 9240)
• Farmall Series (40, 45, 50 with CVT)
• 821F Wheel Loader
• 921F Wheel Loader

1. 1

   Perform a cold soak comparison using a diagnostic scan tool to check the temperature values of the DOC Upstream Temp Sensor, SCR Upstream Temp Sensor, Ambient Air Temp Sensor, and Engine Coolant Temp Sensor before starting the engine in the morning. All temperatures should be nearly identical. If the DOC upstream sensor is reading significantly higher or lower, the sensor is faulty.

2. 2

   Inspect the sensor's electrical connector (X-609, 2-cavity female) for pushed pins, corrosion, or moisture intrusion.

3. 3

   Trace the wiring harness from the DOC sensor back to the ECM to ensure there are no chafed wires shorting to the frame or exhaust heat shields.

1. 1

   Preparation

   Ensure the machine has been turned off and the exhaust system is completely cool to avoid severe burns. Disconnect the negative battery cable.

2. 2

   Locate the Sensor

   Locate the Diesel Oxidation Catalyst (DOC) canister in the exhaust aftertreatment assembly. The upstream temperature sensor is threaded into the exhaust pipe directly before the DOC inlet.

3. 3

   Disconnect

   Unplug the 2-wire electrical connector (X-609).

4. 4

   Removal

   Carefully unscrew the temperature sensor from the exhaust pipe. Note: Exhaust sensors are prone to seizing. Apply penetrating oil to the threads and allow it to soak if the sensor is stuck.

5. 5

   Installation

   Apply a small amount of high-temp anti-seize to the threads of the new sensor (if not already pre-applied from the factory). Thread the new sensor into the exhaust pipe and tighten to OEM torque specifications.

6. 6

   Reconnect

   Plug in the electrical connector, ensuring it clicks securely into place.

7. 7

   Clear Codes

   Reconnect the battery, turn the key to the ON position, and use a diagnostic tool to clear the inactive 3686 fault code. Start the engine and verify the sensor reads correctly as the exhaust heats up.