IAT1, CACT, IAT2 Key-Up Correlation Check

Once the IAT1, CACT, IAT2 are confirmed to be in-range, the key-up correlation test compares the three temperatures on key-up after a long period off key-off time (6 hours). The three-way correlation test is run only once per power-up.

After a long key-off period, the three temperature sensors are expected to report nearly the same temperature. The exception to this is when a block heater is used. Block heater use can cause these three air temperature sensors to widely differ from each other. To detect if an engine coolant heater is active we compare Cylinder Head Temperature (CHT) to Transmission Fluid Temperature (TFT). A significant temperature difference (10°F) indicates block heater activity.

The IAT, CACT, and IAT2 are mounted along the engine air intake system.

• The IAT is mounted in the engine air inlet (near air cleaner).
• The CACT is mounted near the throttle inlet.
• The IAT2 is mounted inside the intake manifold.

If the sensors all agree, no malfunction is indicated and the test is complete. Specifically, the three way check compares 3 sensor pairings. All three pairings must correlate to pass this test.

• IAT and CACT agree within a tolerance (±30°F) and
• CACT and IAT2 agree within a tolerance (±30°F) and
• IAT2 and IAT agree within a tolerance (±30°F).

Case 1  At least two correlation pairings are within tolerance (±30°F). All sensors pass.

Case 2  One correlation pairing is within tolerance (±30°F). Those two sensors that correlate pass, the third sensor is flagged as faulted.

Case 3  Zero correlation pairings are within tolerance (±30°F). P00CE Intake Air Temperature Measurement System - Multiple Sensor Correlation