Case IH F-172-14 - ECU – Engine Control Unit (ECU A-028): Plausibility check error of the intake manifold air temperature sensor at cold start.

During a cold engine start, the Engine Control Unit (ECU) monitors up to five different temperature sensors to check for mutual plausibility (ensuring they all read roughly the same ambient temperature before the engine warms up). If the intake manifold air temperature sensor (designated as Sensor B-185) provides a temperature value that is highly implausible compared to the other sensors, the ECU logs this fault code.

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1. 1

   Ensure the ignition switch is in the OFF position before beginning diagnostics.

2. 2

   Disconnect the electrical connector (X-185) from the intake air temperature/humidity sensor (B-185) and measure the resistance across pin 1 and pin 3. The resistance should be approximately 2.5 kΩ at 20.0 °C (68.0 °F).

3. 3

   If the measured resistance is out of specification, the sensor has failed internally and must be replaced.

4. 4

   If the sensor tests good, visually inspect the wiring harness and connectors between the sensor (X-185) and the ECU (A-028). Look for damaged, bent, or pushed-back pins, corroded terminals, or broken wires. Flex the harness while monitoring a multimeter to check for intermittent breaks or shorts.

5. 5

   If the wiring and sensor are both good, verify that the appropriate software is installed on ECU A-028, and reinstall or flash it if necessary.

1. 1

   Turn the machine off, remove the key, and allow the engine to cool completely.

   This is crucial since the code evaluates cold-start conditions.

2. 2

   Locate the intake manifold air temperature/humidity sensor (B-185) on the engine's air intake path.

3. 3

   Depress the locking tab and disconnect the electrical harness connector (X-185) from the sensor.

4. 4

   Remove the faulty sensor from the intake manifold.

5. 5

   Install the new replacement sensor.

   Ensure it is threaded properly and tightened to standard torque specifications to prevent boost leaks.

6. 6

   Reconnect the electrical harness.

   Ensure the connector clicks and is fully seated.

7. 7

   Turn the ignition ON and use the in-cab monitor or a diagnostic scan tool to clear the F-172-14 fault code.

8. 8

   Perform a cold start of the engine and observe the monitor.

   Verify that the intake manifold temperature reads normally and the fault code does not return.