Case IH 3602 – Engine Control Unit (ECU) / Dosing Control Unit (DCU): Defect ratio between threshold limits - Catalyst Temperature Sensor Circuit

The engine's control module has detected an implausible reading from the upstream catalyst temperature sensor (Bank 1, Sensor 1 - located before the Diesel Oxidation Catalyst / SCR). The temperature reading is outside the expected threshold ratio when compared to other sensors, pointing to a failing sensor, a wiring harness issue, or an exhaust anomaly.

• Magnum series
• Steiger
• Puma
• Optum
• Farmall
• Axial-Flow 7230
• Axial-Flow 8230
• Axial-Flow 9230
• 621F
• 721F
• 821F
• 921F
• 580N EP

1. 1

   Perform a cold soak comparison using the CNH Electronic Service Tool (EST) to check live data for the upstream, downstream, and ambient air temperature sensors (they should read approximately the same).

2. 2

   Inspect the wiring harness leading to the upstream catalyst temperature sensor for melted wires, chafing against the exhaust, or physical damage.

3. 3

   Disconnect the sensor and inspect the connector pins for moisture, corrosion, or pushed-back pins.

4. 4

   Use a multimeter to check the sensor circuit for a short to ground, short to power, or an open circuit between the sensor connector and the ECU/DCU harness.

5. 5

   Inspect the exhaust piping before the DOC/catalyst for severe leaks, which can introduce cold air and skew temperature readings.

1. 1

   Verify the Fault

   Connect the CNH EST diagnostic tool to confirm that code 3602 / P0425 is active or has a high occurrence count.

2. 2

   Locate the Sensor

   Identify the upstream catalyst temperature sensor. It is threaded into the exhaust pipe just before the Diesel Oxidation Catalyst (DOC) / SCR assembly.

3. 3

   Remove the Sensor

   Disconnect the electrical connector. Carefully unthread the sensor from the exhaust bung. Note: Exhaust sensors can be seized; applying penetrating oil and allowing it to soak may prevent thread damage.

4. 4

   Install the New Sensor

   Apply a small amount of high-temperature anti-seize to the threads of the new sensor (avoid getting any on the sensor probe itself). Thread it into the exhaust and tighten to OEM torque specifications.

5. 5

   Reconnect Wiring

   Plug the electrical connector back in, ensuring the locking tab clicks into place. Secure the wire away from direct heat sources using high-temp zip ties if necessary.

6. 6

   Clear Codes and Test

   Use the diagnostic tool to clear the 3602 fault code. Start the engine and monitor the live temperature data as the exhaust heats up to verify the sensor is reading smoothly and accurately. Perform a stationary forced regeneration if required by the service manual to validate the repair.