Case IH 3838 – Engine Control Module (ECM): Upstream oxidation catalyst temperature sensor voltage is lower than expected

The control module is receiving a voltage signal from the Diesel Oxidation Catalyst (DOC) inlet temperature sensor that falls below the normal operating range. This condition is typically caused by a short to ground in the sensor wiring, a disconnected plug, or an internal failure of the sensor itself.

• Steiger T4B
• 240 Series Axial-Flow Combines
• Farmall Series (65C, 95U, 105U, 115U Pro EP)
• Maxxum Series (110, 115, 135, 145, 150)
• Puma Series (200, 240)
• Magnum Series (235, 260, 290, 315, 340, 370)

1. 1

   Visually inspect the DOC inlet temperature sensor wiring harness for chafing, melting from exhaust heat, or pinch points that could cause a short to ground.

2. 2

   Disconnect the sensor and inspect the connector pins for corrosion, moisture, or pushed-out terminals.

3. 3

   Perform a cold soak test using a diagnostic scan tool to check live data for the DOC upstream temperature. After sitting overnight, it should closely match ambient air temperature. An impossibly low default value indicates an open or shorted circuit.

4. 4

   Use a multimeter to check the resistance of the sensor itself. An open circuit (infinite resistance) or a dead short indicates the sensor is internally faulty.

1. 1

   Cool down exhaust system

   Park the machine on a level surface, turn off the engine, and allow the exhaust system to cool completely to avoid severe burns.

2. 2

   Locate sensor

   Locate the upstream DOC temperature sensor on the exhaust assembly.

3. 3

   Disconnect wiring

   Disconnect the sensor's electrical connector from the main engine wiring harness.

4. 4

   Remove faulty sensor

   Using a suitable wrench or an exhaust temperature sensor socket, carefully unscrew the faulty sensor from the exhaust pipe or support bracket. (Penetrating oil may be required if the sensor is seized from heat cycles).

5. 5

   Prepare new sensor

   Apply a small amount of high-temperature anti-seize compound to the threads of the new sensor (if it does not come pre-coated). Be careful not to get any compound on the sensor probe itself.

6. 6

   Install new sensor

   Thread the new sensor into the exhaust pipe and tighten to the manufacturer's torque specification.

7. 7

   Reconnect wiring

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

8. 8

   Clear fault code

   Connect a diagnostic scan tool, clear the 3838 (DTC 2999) fault code from the ECM, and start the engine.

9. 9

   Verify repair

   Monitor the DOC inlet temperature live data to verify the sensor is reading correctly as the exhaust heats up.