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Code Chart 23:

IAT 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 DTC 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 -35°C (-31°F).
OR
^ Signal voltage indicates IAT greater than 146°C (294°F).

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. If CKT 452 is open, there may also be other DTC's 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 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 withing 5 degrees of the ambient. If not, check the IAT sensor using the DIAGNOSTIC AID on the chart. If sensor is OK check connections. If connections at sensor and ECM are OK, replace ECM.