Case IH 3839 – Engine Control Unit (ECU): OxiCat upstream temperature sensor: Diagnostic fault check for SRC low in Oxidation Catalyst upstream temperature

The Engine Control Unit has detected that the signal voltage from the exhaust gas temperature sensor located just upstream of the Oxidation Catalyst (DOC/OxiCat) has dropped below the minimum acceptable threshold, indicating a short to low source or a short to ground in the sensor circuit.

• Farmall
• skid steer
• Farmall 100C
• Farmall 105A/C/U
• Farmall 110A/C/U
• Farmall 115A/C/U
• Farmall 120U
• Farmall 130A
• Farmall 140A
• Maxxum 120
• Maxxum 125
• Maxxum 130
• Maxxum 140
• Maxxum 150
• Puma 130
• Puma 140
• Puma 145
• Puma 170
• Puma 185
• Puma 200
• Puma 215
• Puma 220
• Puma 230
• Puma 240
• Steiger 350-620
• Quadtrac 350-620
• Rowtrac 350-620
• Combine 5130
• Combine 5140
• Combine 7130
• Combine 7140
• Combine 7230
• Combine 7240
• Combine 9230
• Combine 9240
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)

1. 1

   Monitor live data using a diagnostic tool for implausibly low exhaust temperature readings or a pinned minimum value.

2. 2

   Visually inspect the wiring harness leading to the upstream OxiCat temperature sensor for chafed wires, melted insulation, or pinched wires causing a short to ground.

3. 3

   Disconnect the sensor and check the supply and signal voltage at the harness connector.

4. 4

   Measure the sensor's internal resistance with a multimeter; a near-zero ohm reading indicates an internal short.

5. 5

   Check the harness side for continuity to ground on the signal wire to rule out a wiring short between the sensor and the ECU.

1. 1

   Preparation

   Ensure the machine is turned off and the exhaust system has completely cooled down to prevent severe burns.

2. 2

   Locate the Sensor

   Locate the Oxidation Catalyst (DOC) in the exhaust aftertreatment system. Identify the temperature sensor threaded into the exhaust pipe upstream (before) the catalyst.

3. 3

   Disconnect

   Unplug the electrical connector for the sensor from the main engine wiring harness.

4. 4

   Removal

   Using a specialized sensor socket or a flare-nut wrench, carefully unthread the temperature sensor from the exhaust pipe. (Penetrating oil may be required if the sensor is seized from heat cycling).

5. 5

   Installation

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

6. 6

   Reconnect

   Plug the sensor connector back into the engine wiring harness, ensuring the locking tab clicks into place. Secure any loose wiring with high-temp zip ties away from the hot exhaust pipe.

7. 7

   Clear Codes

   Turn the key to the ON position, connect the diagnostic tool, and clear fault code 3839. Start the engine and verify that the live exhaust temperature data is reading correctly and the code does not return.