Case IH 19826 (F-4766-03) – Engine Control Module (ECM / ECU): Downstream oxidation catalyst temperature sensor voltage is higher than expected.

The Engine Control Module (ECM) is receiving a voltage signal from the temperature sensor located after the Diesel Oxidation Catalyst (DOC) that exceeds the normal operating parameters. This typically indicates an open circuit, a short to battery voltage, or a completely failed internal sensor element.

• VESTRUM CVX
• Austoft 9900 Sugarcane Harvesters
• T7 Series Tractors
• Farmall Series (110U, 115U, 120U)
• N-Series Loader Backhoes and Skid Steers (SR175)

1. 1

   Inspect the downstream DOC temperature sensor and its wiring harness for physical damage, melting, or chafing against hot exhaust components.

2. 2

   Disconnect the sensor connector and inspect for corrosion, pushed-out pins, or moisture. Ensure it is securely plugged in.

3. 3

   Use a multimeter to check the sensor's resistance. An infinite resistance (OL) indicates an internal open circuit in the sensor probe.

4. 4

   Check the wiring harness from the sensor connector back to the ECM for continuity.

5. 5

   Check the signal wire for a short to battery voltage, which directly causes the 'voltage higher than expected' condition.

6. 6

   Use the CNH Electronic Service Tool (EST) or a compatible scanner to monitor live data for the downstream DOC temperature. A default extreme value (e.g., -40°C) indicates a compromised circuit.

1. 1

   Preparation

   Turn off the machine, remove the key, and allow the exhaust system (specifically the Diesel Oxidation Catalyst) to cool completely to avoid severe burns.

2. 2

   Locate the Sensor

   Identify the downstream oxidation catalyst temperature sensor, which is located on the exhaust pipe immediately after the DOC unit.

3. 3

   Disconnect Wiring

   Carefully unplug the electrical connector from the sensor to the main engine harness.

4. 4

   Remove the Sensor

   Use a suitable wrench or specialized sensor socket to unscrew the temperature sensor from the exhaust bung. Apply penetrating oil if the sensor is seized due to heat cycling.

5. 5

   Install the New Sensor

   Apply a small amount of high-temp anti-seize compound to the threads of the new sensor (if not pre-applied), being careful not to get any on the sensor probe itself. Thread it into the exhaust bung and tighten to the manufacturer's specified torque.

6. 6

   Reconnect Wiring

   Plug the electrical connector back into the harness, ensuring it clicks and locks securely. Route the wire away from direct heat sources.

7. 7

   Clear Codes and Test

   Turn the key on, connect the diagnostic tool, and clear the inactive 19826 fault code. Start the engine and monitor the live temperature data to ensure the sensor is reading correctly as the exhaust warms up.