Case IH 19199 – Engine Control Unit (ECU) or Vehicle Control Module (VCM): Plausibility check error of the third fresh air temperature sensor at cold start

During a cold engine start, the control module compares the readings of various temperature sensors to verify they are reading similar ambient temperatures. If the third fresh air temperature sensor reports a value that deviates significantly from the expected ambient baseline or the other sensors, it fails the plausibility check and triggers this code.

• Tier 4b
• Case N-series TLBs
• Case IH Farmall 40
• Case IH Farmall 45
• Case IH Farmall 50

1. 1

   Connect a diagnostic service tool and monitor the live data for all temperature sensors during a cold start.

2. 2

   Compare the reading of the third fresh air temperature sensor against the ambient temperature and the other fresh air sensors.

3. 3

   Check for related codes (19202, 19200/19201). If multiple sensors are reading implausibly, the issue is likely a shared ground or ECU supply voltage issue rather than a single failed sensor.

4. 4

   Inspect the sensor's wiring harness for open circuits, short circuits to ground, or short circuits to power.

1. 1

   Power Down

   Turn off the machine and disconnect the battery to prevent electrical shorts during repair.

2. 2

   Locate the Sensor

   Locate the third fresh air temperature sensor (often integrated into the intake air ducting, cab HVAC ducting, or the ambient air/humidity sensor module). If your specific model maps 19199 to the oil temperature sensor, locate the engine oil temp sensor instead.

3. 3

   Inspect the Connection

   Disconnect the sensor connector and inspect for corrosion, moisture, or damaged pins.

4. 4

   Test the Harness

   Test the circuit continuity from the sensor connector back to the ECU/VCM. Repair any chafed or broken wiring.

5. 5

   Replace the Sensor

   If the wiring is intact and the sensor is providing an implausible resistance reading, remove and replace the fresh air temperature sensor.

6. 6

   Reassemble and Clear

   Reconnect the harness and battery. Use the diagnostic service tool to clear the inactive fault codes.

7. 7

   Verify Repair

   Let the machine sit until the engine is completely cold, then perform a cold start to verify the code does not return.