New Holland 3685 – ECU: Exhaust temperature : Fault Check for enhanced SRC-Min of Second exhaust gas temperature

The Engine Control Unit performs a model-based plausibility check that compares the actual measured exhaust temperature against a calculated expected temperature. This fault code triggers when the second exhaust gas temperature sensor (EGT 2) reports a value that falls below the minimum expected threshold. This condition typically points to a faulty sensor, damaged wiring causing a gain offset, or an actual internal engine condition preventing the exhaust from reaching the expected temperature.

• T6 Series
• T6.120
• T6.180
• T7 Series
• T7.165
• T7.270
• T8 Series
• T8.320
• T8.435
• CR Series Combines
• CR7.90
• CX Series Combines
• CX8.90
• FR Forage Cruisers
• Loader Backhoes
• B90B
• B115B

1. 1

   Visually inspect the wiring harness and connectors leading to the second exhaust gas temperature sensor (typically located after the turbocharger or near the DOC/DPF/SCR module) for bad electrical wiring, damaged wire isolation, or corroded connectors.

2. 2

   Disconnect the sensor and check the connector pins for proper contact and isolation.

3. 3

   Use a diagnostic scan tool to monitor live data for the EGT sensors. Compare the reading of the second sensor with the first sensor and ambient temperature when the engine is cold; they should be nearly identical.

4. 4

   Rule out actual mechanical engine issues that could cause abnormally low exhaust temperatures, as the failure can be caused if the real exhaust temperature differs from the calculated one due to an internal engine fault.

1. 1

   Cool 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 EGT 2 sensor

   Locate the second exhaust gas temperature sensor on the exhaust aftertreatment system (often designated as T4 after the turbocharger, or T5/T6 near the DOC/DPF/SCR module).

3. 3

   Disconnect sensor

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

4. 4

   Apply penetrating oil

   Spray penetrating oil on the threads of the sensor where it threads into the exhaust pipe, and allow it to sit to prevent thread damage during removal.

5. 5

   Remove faulty sensor

   Using an appropriate wrench, carefully loosen and remove the faulty EGT sensor.

6. 6

   Inspect and clean threads

   Inspect the mounting port threads in the exhaust pipe and clean them if necessary.

7. 7

   Apply anti-seize

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

8. 8

   Install new sensor

   Thread the new sensor into the exhaust pipe by hand to prevent cross-threading, then tighten it to the OEM specified torque.

9. 9

   Reconnect electrical connector

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

10. 10

    Clear code and verify

    Connect a diagnostic scan tool, clear the 3685 fault code, and run the engine through a standard operating cycle to verify the code does not return and live temperature readings are accurate.