Case IH F-4765-00 - ECU – Engine ECU: Upstream oxidation catalyst temperature sensor voltage is higher than expected.

The engine control system is reading a voltage signal from the Diesel Oxidation Catalyst (DOC) inlet temperature sensor that exceeds the normal operating range. This condition is typically caused by an open circuit (such as a broken wire or disconnected plug), a short to a high-voltage power source, or an internal failure of the sensor itself.

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1. 1

   Locate the upstream DOC temperature sensor on the exhaust aftertreatment system and inspect the sensor's wiring harness for chafing, melting, or breaks.

2. 2

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

3. 3

   Use a multimeter to check the sensor's signal wire for a short to power (which causes the high voltage condition) or an open circuit.

4. 4

   Measure the resistance across the sensor's terminals. If the sensor reads completely open (infinite resistance), it has failed internally and must be replaced.

1. 1

   Safety First

   Ensure the machine is turned off and the exhaust system has completely cooled down, as the DOC and surrounding components operate at extremely high temperatures.

2. 2

   Disconnect

   Unplug the electrical connector from the upstream oxidation catalyst temperature sensor.

3. 3

   Removal

   Using the appropriate wrench or specialized sensor socket, carefully unthread the faulty temperature sensor from the exhaust pipe/catalyst housing. (Penetrating oil may be required if the sensor is seized from heat cycling).

4. 4

   Installation

   Apply a small amount of high-temperature anti-seize to the threads of the new sensor (if not already pre-applied by the manufacturer). Thread the new sensor into the housing and tighten it to the OEM torque specification.

5. 5

   Reconnect

   Plug the electrical connector back into the machine's wiring harness, ensuring it clicks securely into place.

6. 6

   Clear and Verify

   Turn the machine's ignition on. Use a diagnostic scan tool to clear the F-4765-00 fault code from the Engine ECU. Start the engine and monitor the exhaust temperature readings to verify the code does not return and the sensor is reading accurately.