Powertrain Controls - ECM/PCM

DTC 23 Intake Air Temperature (IAT) Sensor Circuit High (Low Temperature Indicated):

Intake Air Temperature (IAT) Sensor Circuit:

Circuit Description
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.

DTC 23 Will Set When
^ A signal voltage indicates an Intake Air Temperature (IAT) below -40°C (-22°F) for 60 seconds.
^ Time since engine start is 4 minutes or longer.
^ No VSS (vehicle not moving).

Action Taken (PCM will default to)
The Malfunction Indicator Lamp (MIL) will illuminate.

DTC 23 Will Clear When
Conditions for fault are no longer present and Tech 1 "Clear DTCs" function is used or 50 ignition switch key cycles have passed with no further faults or ignition switch is turned "OFF" and fuse #9 (ECM B) fuse is removed for 10 seconds.

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

1. This step will determine if DTC 23 is the result of a hard failure or an intermittent condition.

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 "Intermittents." - Intermittent Malfunctions

The "Temperature to Resistance Value" scale at the right 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.