Case IH 19825 – Engine Control Module (ECM / Engine ECU): Downstream oxidation catalyst temperature is too high.

The temperature sensor located downstream of the Diesel Oxidation Catalyst (DOC) is registering an exhaust gas temperature that exceeds the maximum safe operating limit. This can be caused by a faulty sensor, wiring issues, or a physical issue such as improper fuel oxidation inside a damaged DOC causing uncontrolled heat spikes.

• Tier 4b
• Magnum 235
• Magnum 250
• Magnum 260
• Magnum 280
• Magnum 290
• Magnum 310
• Magnum 340
• Magnum 370
• Magnum 380
• Farmall 90
• Farmall 110A
• Puma
• Optum
• Axial-Flow 7230
• Axial-Flow 8230
• Axial-Flow 9230
• N-Series Loaders
• 521G
• 621G
• 721G
• 821G
• 921G

1. 1

   Check Associated Fault Codes: Look for related voltage codes (e.g., 19826 for short circuit/sensor failure, or 19827/19828 for upstream temperature faults).

2. 2

   Inspect the Wiring Harness: Check the 2-pole electrical connector and wiring harness leading to the downstream temperature sensor for melting, chafing, or corrosion.

3. 3

   Inspect the DOC for Internal Damage: Check for exhaust restriction, sluggish engine response, or signs of internal melting/collapse of the catalyst substrate caused by improper fuel oxidation.

4. 4

   Verify Dosing Conditions: Ensure the system isn't over-dosing due to a skewed sensor reading (requires a minimum exhaust temperature of 220°C - 240°C / 428°F - 464°F on both upstream and downstream sensors).

1. 1

   Turn off the machine and disconnect the battery.

   Allow the exhaust system to cool completely to avoid severe burns.

2. 2

   Locate the downstream DOC temperature sensor.

   Locate the sensor on the SCR muffler/exhaust outlet pipe assembly, just after the NOx sensor.

3. 3

   Disconnect the electrical connector.

   Disconnect the 2-pin electrical connector from the sensor harness.

4. 4

   Remove the temperature sensor.

   Using a 17mm spanner/wrench, carefully unthread the temperature sensor from the exhaust pipe.

5. 5

   Remove the SCR muffler/catalyst (if necessary).

   If replacing the entire SCR muffler/catalyst due to internal melting, remove the upper heat shields and the clamps securing the SCR muffler to the exhaust outlet pipe.

6. 6

   Prepare the new sensor.

   Apply a high-temperature anti-seize compound to the threads of the new sensor (if not pre-applied).

7. 7

   Install the new sensor.

   Thread the new sensor into the exhaust pipe and tighten. Torque the temperature sensor to 27 – 30 N·m (20 – 22 lb ft).

8. 8

   Reconnect the electrical harness.

   Ensure it is routed away from direct heat sources.

9. 9

   Clear fault codes and verify operation.

   Clear the fault codes via the diagnostic service tool and run the engine to verify that the downstream temperature reads within normal parameters.