Case IH 3838 (DTC 2999) - ECU – Engine Control Unit (ECU) / Engine Control Module (ECM): Upstream oxidation catalyst temperature sensor voltage is lower than expected.

The Engine Control Unit (ECU) is reading a lower-than-expected voltage signal from the temperature sensor located upstream of the Diesel Oxidation Catalyst (DOC) in the exhaust aftertreatment system. A low voltage reading typically indicates a short to ground in the sensor's wiring circuit or an internally shorted/failed sensor.

• MAXXUM T4E
• 240 Series Axial-Flow Combines
• Farmall Tractors: 40, 45, 50, 90C, 100C, 110C, and 120C
• Magnum Tractors

1. 1

   Connect a diagnostic tool (like the EST or PT-Box tool) to verify if the fault is currently present and active.

2. 2

   Look for associated codes that might point to a broader issue, such as DTC 1899 (sensor voltage is higher than expected) or DTC 352C (comparison to a calculated temperature value failure).

3. 3

   Inspect the upstream oxidation catalyst temperature sensor to ensure it is installed, correctly mounted, and not physically damaged.

4. 4

   Inspect the wiring harness between the sensor and the ECU for chafing, melting, or a short to ground.

5. 5

   Check the ECU connector pins (specifically Pin 1 Signal and Pin 2 Ground) for corrosion, pushed-out pins, or moisture intrusion.

1. 1

   Power Down

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

2. 2

   Locate the Sensor

   Locate the upstream oxidation catalyst (DOC) temperature sensor on the exhaust aftertreatment system piping (before the DOC canister).

3. 3

   Disconnect

   Unplug the sensor's wiring harness connector.

4. 4

   Test/Repair Wiring

   Test the sensor resistance and wiring continuity. If the wiring harness is shorted to ground, repair or replace the damaged section of the harness.

5. 5

   Remove Sensor

   If the wiring is intact, the sensor itself has failed. Remove the faulty sensor using an appropriate wrench. (Penetrating oil may be required if the sensor is seized in the exhaust pipe).

6. 6

   Install New Sensor

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

7. 7

   Reconnect

   Reconnect the wiring harness connector securely.

8. 8

   Clear Codes & Reset Inducement

   Reconnect the battery and use the diagnostic tool to clear the fault codes. Crucial Step: Because this emissions fault causes an engine inducement (derate), you must perform an 'Engine Restart Counter Reset / Unlock Inducement' configuration using the diagnostic tool before returning the machine to service.