Part 1 of 2

Code Chart 23 (Part 1 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. Engine has been running for longer than 2 minutes.
b. Signal voltage indicates an IAT temperature less than -38°C (-36°F).

2. This test simulates conditions for a Code 23 (High Temperature Indicated). If the Scan tool displays a high temperature, the ECM and wiring are OK.

3. This step checks continuity of the signal wire and sensor ground wire. If the sensor ground wire is open, there may also be a Code 21.

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 or the sensor wire become open. If Code 23 is intermittent, Testing and Inspection