New Holland ENG 3839 – Engine Control Unit (ECU): Diesel Particulate Filter (DPF) Temperature Sensor: Diagnostic fault check for SRC low in Oxidation Catalyst upstream temperature

The engine control module has detected that the signal voltage from the exhaust gas temperature sensor located upstream (before) the Diesel Oxidation Catalyst (DOC) / DPF assembly is abnormally low. This condition almost always indicates a short circuit to ground, either internally within the sensor itself or within the wiring harness connecting the sensor to the controller.

• L220
• L230
• SR175
• C-Series
• T4
• T5
• T6
• T7
• T8
• CX series

1. 1

   Visually inspect the wiring harness leading to the DOC/DPF upstream temperature sensor for melted insulation, chafing against the exhaust pipe, or pinched wires that could cause a short to ground.

2. 2

   Disconnect the sensor's 2-pin oval connector and check for moisture, soot intrusion, corrosion, or bent pins.

3. 3

   With the sensor disconnected, turn the key to the ON position and use a multimeter to check the reference voltage from the ECU and test the ground circuit for continuity.

4. 4

   Measure the resistance across the sensor's pins. If the resistance reads near zero (shorted) or is completely out of specification for the ambient temperature, the sensor has failed internally.

1. 1

   Preparation

   Turn off the machine, remove the key, and disconnect the negative battery cable. Ensure the exhaust system has completely cooled down to prevent severe burns.

2. 2

   Locate the Sensor

   Locate the upstream exhaust gas temperature sensor. It is threaded into the exhaust pipe directly before the Diesel Oxidation Catalyst (DOC) / DPF canister.

3. 3

   Disconnect

   Unplug the electrical connector from the sensor harness.

4. 4

   Removal

   Using an appropriately sized wrench or specialized sensor socket, carefully unscrew the sensor from the exhaust bung. Note: Exhaust sensors frequently seize due to extreme heat cycles. Apply penetrating oil to the threads and allow it to soak if the sensor is stuck.

5. 5

   Installation

   Apply a small amount of high-temperature anti-seize compound to the threads of the new sensor (if it does not come pre-coated). Be extremely careful not to get any anti-seize on the sensor probe tip, as this will contaminate it.

6. 6

   Torque

   Thread the new sensor in by hand to prevent cross-threading, then tighten it to the manufacturer's specified torque.

7. 7

   Reconnect

   Plug the electrical connector back into the engine harness, ensuring the locking tab clicks into place. Secure the wire away from direct heat sources.

8. 8

   Clear Codes

   Reconnect the battery, turn the ignition on, and use a diagnostic scan tool to clear the ENG 3839 fault code. Start the engine and verify the code does not return.