Case IH 19200 – Engine Control Unit (ECU): Plausibility check error of the forth fresh air temperature sensor at cold start

When a machine has been turned off long enough for the engine to completely cool down (a 'cold soak'), the Engine Control Unit (ECU) expects all temperature sensors to report approximately the same temperature. During the cold start sequence, the ECU runs a plausibility check. If the designated fresh air temperature sensor (or fuel temperature sensor) reports a value that is drastically different from the other sensors, the ECU flags the reading as physically impossible and logs code 19200.

• Tier 4b
• FPT Tier 4 Final and Stage V engines
• Case IH Farmall series (40, 45, 50, 115U)
• Case IH Steiger and Magnum tractors
• CASE Construction equipment (N-Series loaders)

1. 1

   Verify cold soak: Ensure the machine has been sitting with the engine off for at least 8 hours so all components have equalized to the ambient outside temperature.

2. 2

   Compare live data: Connect the CNH Electronic Service Tool (EST) and view the live data for all engine temperature sensors before cranking the engine. Compare the Ambient Air, Intake Air, Coolant, and Fuel temperatures.

3. 3

   Identify the outlier: Look for the sensor that is reading out of range. A failed sensor will typically default to an extreme value (e.g., -40°C or +150°C) or show a value significantly skewed from the actual ambient temperature.

4. 4

   Inspect harness: Once the outlier sensor is identified, inspect its wiring harness. Look for chafed wires, shorts to ground, or a disconnected/corroded connector, which are common causes for implausible voltage readings.

1. 1

   Turn off the ignition key and disconnect the battery ground cable to prevent electrical shorts.

2. 2

   Locate the faulty sensor on the engine.

   Either the fresh air/intake temperature sensor or the fuel temperature sensor on the fuel rail/filter housing, depending on which failed the live data check.

3. 3

   Depress the locking tab and disconnect the electrical harness connector from the sensor.

4. 4

   Clean the area around the sensor base thoroughly to prevent dirt from entering the intake tract or fuel system.

5. 5

   Unthread and remove the faulty sensor.

   Note: If removing the fuel temperature sensor, have a rag ready to catch a small amount of residual diesel fuel.

6. 6

   Thread the new replacement sensor into place and tighten to the OEM torque specification.

7. 7

   Reconnect the electrical harness, ensuring the connector clicks securely into place.

8. 8

   Reconnect the battery ground cable.

9. 9

   Connect the CNH EST diagnostic tool, clear the inactive 19200 fault code, and start the engine to verify the code does not return.