Powertrain Controls - ECM/PCM

DTC 23 Chart:

Wiring Diagram:

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 (about 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:
a. The engine has been running longer than five minute.
b. The signal voltage indicates a IAT reading of less than -25°C (-13°F).
c. Vehicle speed is less than 45 mph.

2. A DTC 23 will set due to an open sensor, wire, or connection. This test will determine if the wiring and ECM are OK.

3. This will determine if the IAT sensor signal circuit 472 or the IAT sensor ground circuit 452 is open.



DIAGNOSTIC AIDS:

^ A "Scan" tool indicates the temperature of the air surrounding the air cleaner because the IAT sensor is mounted to the air cleaner housing.


^ 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.

^ When the ECM detects a fault in the IAT circuit, a default value of 40°C (104°F) will be displayed on the scan tool. After the engine starts, the IAT will increase due to THERMAC operation and underhood temperatures.

^ Carefully check harness routing for possible open in circuit 472 or 452.