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Code Chart 23:

IAT Circuit:

CIRCUIT DESCRIPTION:
The Intake Air Temperature (IAT) sensor, located in the air cleaner assembly, uses a thermistor to control the signal voltage to the ECM. The ECM applies a reference voltage (4.0-5.5 volts) on circuit 472 to the sensor. When the intake 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 and the voltage drops, 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 an IAT reading of less than -34°C (-30°F).
OR
^ The signal voltage indicates an IAT reading greater than 150°C (302°F) for more than 2 seconds.

2. This test simulates conditions for a Code 23. 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. If circuit 452 is open, there may be other codes stored.

DIAGNOSTIC AIDS:
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. If Code 23 is intermittent, Testing and Inspection