Part 2 of 2

Code Chart 23 (Part 2 Of 2):

Intake Air Temperature Sensor Circuit:

CIRCUIT DESCRIPTION:

The Intake Air Temperature (IAT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage (4-6V) on the sensor signal wire to the sensor. When manifold air is cold, the sensor (thermistor) resistance is high, therefore, the ECM will see a high signal voltage. As the air warms, the sensor resistance becomes less, and the voltage drops.

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

1. This step checks to see if Code 23 is the result of a hard failure or an intermittent condition. A Code 23 will set if:

a. An IAT temperature greater than 199°C (390°F) is detected for a time longer than 2 seconds.

DIAGNOSTIC AIDS:

If the engine has been allowed to cool to an ambient temperature (overnight), coolant and IAT temperatures may be checked with a Scan tool and should read close to each other. A Code 23 will result if the signal wire is shorted to ground. If Code 23 is intermittent, Testing and Inspection