New Holland ENG 3994 – ENGINE (ISM-IDI or F5C): Diesel Oxidation Catalyst (DOC) IN Temperature is over 800 °C (1472 °F).

The Exhaust Gas Temperature Sensor (EGTS) located at the inlet of the Diesel Oxidation Catalyst is detecting an exhaust temperature that exceeds the safe operating threshold of 800 °C (1472 °F). This can indicate an actual severe overheating condition in the exhaust aftertreatment system (often during regeneration) or a failed temperature sensor sending a false high-voltage signal.

• L220
• L230
• SR175
• C362
• B90B
• B100B

1. 1

   Check for accompanying sensor circuit codes such as 1800 (Out of Voltage - Low) or 1801 (Out of Voltage - High)

2. 2

   Verify actual temperature using a diagnostic service tool. If it reads over 800 °C immediately upon a cold start, the sensor or wiring is shorted

3. 3

   Inspect the harness and connectors leading to the DOC IN temperature sensor for melted wires, chafing, or a short to ground/power

4. 4

   Investigate mechanical engine conditions that cause excessive exhaust heat, such as leaking fuel injectors, a stuck intake throttle valve, or a severely clogged DPF forcing an uncontrolled regeneration

1. 1

   Locate the Sensor

   Locate the Diesel Oxidation Catalyst (DOC) inlet temperature sensor. It is threaded into the exhaust pipe just before the DOC housing (often designated as the T5 position).

2. 2

   Disconnect

   Unplug the 2-wire electrical connector from the sensor harness.

3. 3

   Remove

   Carefully unscrew the threaded sensor from the exhaust pipe bung. (Penetrating oil may be required if the sensor is seized from heat cycling).

4. 4

   Install

   Thread the new Exhaust Gas Temperature Sensor into the exhaust pipe and tighten to the manufacturer's torque specification.

5. 5

   Reconnect

   Plug the sensor's rectangular connector back into the engine wiring harness.

6. 6

   Clear Codes

   Use a diagnostic tool or CAN-bus DTC eraser to clear the ENG 3994 code from the Engine ECU memory.

7. 7

   Test

   Start the engine and monitor the DOC IN temperature via the service tool to ensure it rises normally and stays well below the 800 °C limit during operation.