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Code Chart 23:

IAT Sensor 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 Engine Control Module (ECM). The ECM applies a reference voltage (4 to 4.5 volts) on CKT 472 to the sensor. When intake air is cold, the sensor (thermistor) resistance is high. The ECM will then sense a high signal voltage. As the air warms, the sensor resistance becomes less and the voltage drops.

TEST DESCRIPTION: Number(s) below refer to circled number(s) on the diagnostic chart.

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

^ Engine running for 2 minutes or longer.
^ Signal voltage indicates an IAT temperature less than -34°C (-3O°F).
OR
^ Signal voltage indicates an IAT temperature greater than 15O°C (302°F) for more than 2 seconds.

2. This test simulates conditions for a DTC 23. If the scan tool displays a high temperature, the ECM and wiring are OK.

3. This step checks continuity of CKT 472 and CKT 469. If CKT 469 is open, DTC 21 may be stored.

DIAGNOSTIC AIDS:
If the engine has been allowed to cool to an ambient temperature (overnight), engine coolant and intake temperatures may be compared with a scan tool and should read close to each other.

^ If DTC 23 is intermittent or a "Hard Start" symptom is present, check intake air temperature with a scan tool on a cool engine. Temperature displayed should be within 5 degrees of the ambient. If not, check the IAT sensor using the "Diagnostic Aids" on the next part. If sensor is OK, check connections.