Powertrain Controls - ECM/PCM

Code 23 Chart:

Wiring Diagram For IAT:

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 Code 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 -28°C (-20°F).
c. Vehicle speed is less than 35 mph.

2. A Code 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 455 is open.


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. After the engine starts, the IAT will increase due to Thermac operation and underhood temperatures.
2. Carefully check harness and connections for possible open circuits 472 or 455. If Code 23 is intermittent, see DIAGNOSIS BY SYMPTOM.
3. A "Scan" tool indicates the temperature of air in the air cleaner housing.