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Code Chart 23:

IAT Sensor Circuit:

CIRCUIT DESCRIPTION:
The Intake Air Temperature (IAT) sensor uses a thermistor that controls the signal voltage to the ECM. The ECM applies a reference voltage (5.0 volts) on circuit 472 to the sensor. When the air is cold, the sensor (thermistor) resistance is high, therefore the ECM will sense a high signal voltage. If the air is warm, the sensor resistance is low, therefore the ECM will see a low voltage.

TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. A Code 23 will set under the following conditions:

^ The engine has been running longer than two minutes.
^ The signal voltage indicates a IAT reading of less than -35°C (-31°F).
OR
^ Signal voltage indicates IAT greater than 150°C (302°F) for more than 2 seconds.

2. If the "Scan" tool displays a high temperature, the ECM and wiring are OK.

3. This step checks the continuity of circuits 472 and 452.

DIAGNOSTIC AIDS:

1. If the engine has been allowed to cool to ambient temperature, coolant and IAT temperatures may be checked with a "Scan" tool. The readings should be close to each other.
2. If circuit 452 is open, there may also be a Code 14, 21, and 66. If Code 23 is intermittent, Testing and Inspection