Case IH 3841 – Engine Control Unit (ECU): Diesel Particulate Filter (DPF) Upstream Temperature Sensor: Diagnostic fault check for SRC low

The Engine Control Unit is detecting a "Source Low" condition from the sensor located just before (upstream of) the Diesel Particulate Filter. This typically points to a short circuit to a low voltage source (short to ground) in the sensor itself or its wiring harness.

• Farmall
• Maxxum
• Puma
• Magnum
• Optum
• Steiger
• Quadtrac
• Quantum
• AF
• AFX

1. 1

   Inspect the wiring harness leading to the DPF upstream temperature sensor for chafing, melting from exhaust heat, or bare wires touching the chassis.

2. 2

   Disconnect the sensor and inspect the pins on both the sensor side and the harness side for corrosion, moisture, or bent pins.

3. 3

   Using a multimeter, check the sensor signal wire for continuity to ground. If the harness is shorted to ground while disconnected from the sensor, the wiring harness is the culprit.

4. 4

   Test the internal resistance of the temperature sensor. If it reads completely open or dead shorted internally, the sensor has failed.

1. 1

   Disconnect Power

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

2. 2

   Access the Sensor

   Locate the DPF upstream temperature sensor on the exhaust aftertreatment assembly (it will be threaded into the exhaust pipe just before the DPF canister).

3. 3

   Remove the Sensor

   Disconnect the electrical pigtail. Use a specialized sensor socket or a flare nut wrench to carefully unthread the sensor from the exhaust bung. (Note: Penetrating oil may be required if the sensor is seized from exhaust heat).

4. 4

   Install the New Sensor

   Apply a small amount of high-temp anti-seize to the threads of the new sensor (avoiding the probe tip). Thread it into the exhaust bung and tighten to OEM torque specifications.

5. 5

   Reconnect Wiring

   Plug the sensor connector back into the engine wiring harness, ensuring it clicks securely into place. Route the wire away from direct heat sources.

6. 6

   Clear Codes and Test

   Reconnect the battery, turn the key on, and use a diagnostic scan tool to clear the 3841 fault code. Start the engine and monitor the exhaust gas temperature readings. A forced stationary DPF regeneration may be required to verify the sensor is reading the temperature ramp-up correctly.