Case IH 3838 – Engine Control Module (ECM) / EDC: OxiCat upstream temperature sensor: Diagnostic fault check for SRC high in Oxidation Catalyst upstream temperature

The control module is receiving a voltage signal from the upstream Oxidation Catalyst (DOC/OxiCat) temperature sensor that exceeds the maximum allowable threshold. This is typically caused by an open circuit, a short circuit to a high-voltage power source, or a completely failed internal sensor resistor.

• Farmall
• skid steer
• Maxxum
• Puma
• Steiger
• Quadtrac
• Optum
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)

1. 1

   Inspect the wiring harness leading to the upstream exhaust temperature sensor for melted wires, chafing against the exhaust pipe, or corrosion inside the connector.

2. 2

   Disconnect the sensor, turn the key to the ON position, and check the supply and signal voltage at the harness connector to ensure the ECM is sending the correct 5V reference and the signal wire is not shorted to the 12V supply.

3. 3

   Measure the internal resistance of the temperature sensor across its pins. If the multimeter reads 'OL' (open loop/infinite resistance), the sensor has failed internally.

1. 1

   Safety First

   Turn off the machine, allow the exhaust system to cool completely, and disconnect the negative battery cable to prevent electrical shorts.

2. 2

   Locate the Sensor

   Locate the upstream Oxidation Catalyst (DOC) temperature sensor. It is threaded directly into the exhaust pipe just before the DOC/DPF aftertreatment assembly.

3. 3

   Disconnect

   Unplug the electrical pigtail connector linking the sensor to the main engine wiring harness.

4. 4

   Removal

   Using a properly sized wrench or O2/temperature sensor socket, carefully unscrew the sensor from the exhaust pipe. Penetrating oil may be required to free the threads without stripping them.

5. 5

   Installation

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

6. 6

   Reconnect

   Plug the sensor's electrical connector back into the engine harness.

7. 7

   Clear Codes

   Reconnect the battery, turn the ignition on, and use an Electronic Service Tool (EST) or compatible OBD scanner to clear the 3838 fault code.

8. 8

   Validation

   Start the engine and monitor the live exhaust temperature data to ensure the sensor is reading ambient/rising exhaust temperatures correctly and that the code does not return.