Case IH 19427 – Engine Control Unit (ECU): Plausibility temperature monitoring with upstream temperature

The exhaust gas temperature sensor located upstream of the catalyst (DOC or SCR) is providing an 'implausible' reading that does not align with the expected (modeled) temperature calculated by the engine control system or conflicts with the readings from the downstream temperature sensor.

• Tier 4b
• Steiger series tractors
• Magnum series tractors
• Puma series tractors
• Optum series tractors
• Farmall series tractors
• AFX series combines
• N-Series Loaders

1. 1

   Cold Soak Comparison: Let the engine cool down completely. Use the CNH Electronic Service Tool (EST) to monitor the live data of all exhaust temperature sensors. When cold, the upstream temperature, downstream temperature, and ambient air temperature should all read approximately the same. A drifted sensor will show a significant variance.

2. 2

   Wiring and Connector Inspection: Check the wiring harness and the sensor connector (often a 2-cavity female connector) for physical damage, melted wires, or oxidation on the contact pins.

3. 3

   Open Circuit Test: Disconnect the upstream temperature sensor while monitoring the service tool. The system should immediately flag an open circuit/SRC high fault for that specific sensor. If it does not, there is a wiring harness short to the ECU.

4. 4

   Exhaust Leak Check: Inspect the exhaust piping between the turbocharger and the upstream temperature sensor. An exhaust leak can introduce cooler ambient air or allow hot gases to escape, causing an artificially low (implausible) temperature reading.

1. 1

   Cool Down

   Ensure the machine is parked on a level surface, turned off, and the exhaust system has completely cooled to prevent severe burns.

2. 2

   Locate the Sensor

   Locate the upstream temperature sensor. Depending on the specific emissions layout, this will be threaded into the exhaust pipe immediately before the Diesel Oxidation Catalyst (DOC) or the Selective Catalytic Reduction (SCR) chamber.

3. 3

   Disconnect Wiring

   Unplug the 2-pin electrical connector linking the sensor to the engine wiring harness.

4. 4

   Remove the Sensor

   Spray penetrating oil around the base of the sensor threads if it appears rusted or seized. Carefully use a line wrench or specialized sensor socket to unthread the sensor from the exhaust bung.

5. 5

   Install the New Sensor

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

6. 6

   Reconnect and Clear

   Reconnect the electrical harness. Connect the CNH EST diagnostic tool, clear the 19427 fault code, and perform a forced regeneration or a test drive under load to ensure the exhaust temperatures rise plausibly and the code does not return.