Case IH 19426 – Engine Control Unit (ECU) or Dosing Control Unit (DCU): Plausibility temperature monitoring with downstream temperature

The control module has detected an implausible reading from the downstream Exhaust Gas Temperature (EGT) sensor located in the Selective Catalytic Reduction (SCR) / exhaust aftertreatment system. The sensor is providing a reading that does not logically align with the engine's current operating conditions, the ambient temperature, or the readings from the upstream temperature sensor, which will eventually force the machine into a power derate or limp mode.

• Tier 4b
• Farmall (100C through 120U)
• Maxxum (120-140)
• Puma
• Magnum
• Steiger
• Axial-Flow 7120
• Axial-Flow 7230
• Axial-Flow 8230
• Axial-Flow 9230
• N-Series Loader Backhoes
• SR/SV Series Skid Steers
• SR270

1. 1

   Cold Soak Temperature Comparison: Let the machine sit turned off until the engine and exhaust are completely cooled to ambient temperature. Use the Case IH Electronic Service Tool (EST) or diagnostic display to read the upstream and downstream EGT sensors. Both sensors should read the exact same ambient temperature. If the downstream sensor reads significantly higher or lower, the sensor is faulty.

2. 2

   Visual Wiring Inspection: Inspect the wiring harness leading to the downstream EGT sensor. Look for melted wires, chafing against the frame, or corrosion inside the connector, which can cause high resistance and false temperature readings.

3. 3

   Resistance Testing: Disconnect the sensor and measure the resistance across the sensor pins using a multimeter. If the multimeter reads an open circuit (infinite resistance) or a dead short, the sensor has failed internally.

1. 1

   Safety First

   Turn off the machine, disconnect the battery master switch, and allow the exhaust system to cool completely to avoid severe burns.

2. 2

   Locate the Sensor

   Locate the downstream Exhaust Gas Temperature sensor. It is threaded into the exhaust pipe/catalyst canister after the DOC/DPF or SCR catalyst.

3. 3

   Disconnect Harness

   Unplug the electrical connector for the sensor and unclip the wire from any retaining brackets.

4. 4

   Remove the Sensor

   Apply penetrating oil to the threads of the sensor if it is rusted. Use a line wrench or specialized sensor socket to carefully unthread the sensor from the exhaust pipe.

5. 5

   Install the New Sensor

   Apply a small amount of high-temperature anti-seize compound to the threads of the new sensor (if it does not come pre-applied). Thread it in by hand to prevent cross-threading, then tighten to the OEM torque specification.

6. 6

   Reconnect

   Plug the electrical connector back in and ensure the wire is secured away from hot exhaust components.

7. 7

   Clear Codes

   Connect the Case IH Electronic Service Tool (EST) laptop to clear the fault codes and reset the SCR system. If the machine was in a hard derate/limp mode, a software reset or a forced stationary regeneration may be required to restore full power.