Case IH 3836 (F-4766-04) – Engine Control Module (ECM): Downstream oxidation catalyst temperature sensor voltage is lower than expected.

The signal voltage returning from the temperature sensor located downstream of the Diesel Oxidation Catalyst (DOC) has dropped below the minimum acceptable threshold. This condition is typically caused by a short to ground in the sensor's wiring circuit, a disconnected plug, or an internal failure of the sensor itself.

• VESTRUM CVX
• Case IH Farmall series (e.g., 40-45-50, 115U)
• Case IH Puma and Steiger series tractors
• Case IH Axial-Flow Combines (e.g., 240 series)
• Case N-Series Loaders and TLBs

1. 1

   Use a diagnostic service tool to confirm if the fault is currently active or stored (inactive may indicate an intermittent wiring issue)

2. 2

   Visually inspect the downstream oxidation catalyst temperature sensor body, connector, and wiring harness for melting, chafing, corrosion, or physical damage

3. 3

   Disconnect the sensor and check the harness side for a short to ground using a multimeter

4. 4

   Check the ECM supply voltage to the sensor to ensure the 12/24V actuator supply is not shorted

5. 5

   Measure the resistance across the sensor's pins to check for an open or internally shorted thermistor

1. 1

   Power Down

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

2. 2

   Locate the Sensor

   Identify the downstream temperature sensor on the Diesel Oxidation Catalyst (DOC) housing. (Do not confuse this with the upstream sensor).

3. 3

   Disconnect and Remove

   Unplug the sensor's electrical connector. Use a specialized sensor socket or wrench to carefully unthread the sensor from the exhaust bung. Apply penetrating oil prior to removal if necessary.

4. 4

   Harness Repair (If Applicable)

   If the diagnostic checks revealed a short to ground in the wiring harness, repair the damaged wires or replace the affected harness section.

5. 5

   Install New Sensor

   Apply a small amount of anti-seize compound to the threads of the new sensor (if not pre-applied by the manufacturer). Thread the sensor into the exhaust bung and tighten to the OEM torque specification.

6. 6

   Reconnect

   Plug the sensor connector back into the engine wiring harness. Reconnect the battery.

7. 7

   Clear Codes

   Connect a diagnostic service tool, clear the 3836 (F-4766-04) fault code, and run the engine through a standard operating cycle to ensure the code does not return and the sensor reads the correct exhaust temperatures.