Powertrain Controls - ECM/PCM

DTC 23 Diagnostic Chart:

Intake Air Temperature Sensor Circuit:

CIRCUIT DESCRIPTION:
The Intake Air Temperature (IAT) sensor is a thermistor that controls the signal voltage to the Powertrain Control Module (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.

CHART TEST DESCRIPTION:
Numbers below refer to circled numbers on the diagnostic chart.
1. This step will determine if DTC 23 is the result of a hard failure or an intermittent condition.
^ DTC 23 will set if all conditions are met:
- A signal voltage indicates an 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 DTC 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 Diagnosis by Symptom/Intermittents.
- Intermittent Malfunctions
The "Temperature to Resistance Value" scale within the diagnostic chart 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.