Part 2 of 2

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. This step determines if Code 23 is the result of a hard failure or an intermittent condition.

2. If the ECM recognizes the open circuit (high voltage) and displays a low temperature, the ECM and wiring are OK.

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 Code 23 is intermittent, Testing and Inspection