Powertrain Controls - ECM/PCM

DTC 23 (IAT) Chart:

IAT Sensor Circuit:

Circuit Description:
The The Intake Air Temperature (IAT) sensor is a thermistor that controls the signal voltage to the PCM. The PCM applies a voltage (4-6 volts) on CKT 472 to the sensor. When the air is cold, the sensor (thermistor) resistance is high, therefore, the PCM will see a high signal voltage. If the air is warm, the sensor resistance is low, therefore, the PCM will see a low voltage.

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. This step will determine if Code 23 is the result of a hard failure or an intermittent condition. Code 23 will set if all conditions are met:
^ A signal voltage indicates a Intake Air Temperature (IAT) below -30°C (-22°F) for 25 seconds.
^ Time since engine start is 4 minutes or longer.
^ No VSS (vehicle not moving)

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

3. This will determine if the signal CKT 472 or the 5 volt return CKT 455 is open.


Diagnostic Aids:
A Tech 1 "Scan" tool reads temperature of the air entering the engine and should read close to ambient air temperature when engine is cold, and rises as underhood temperature increases.

Carefully check harness and connections for possible open CKT 472 or 455. Refer to "Driveablity Symptoms," for "Intermittents"

The "Temperature to Resistance Value" scale may be used to test the IAT sensor at various temperature levels to evaluate the possibility of a "skewed" (mis-scaled) sensor. A "skewed" sensor could result in poor driveability complaints.