Powertrain Controls - ECM/PCM

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

Intake Air Temperature Sensor Wiring Circuit:

Circuit Description:
The Intake Air Temperature (IAT) sensor uses a thermistor to control the signal voltage at the Powertrain Control Module (PCM). The PCM applies a voltage (about 5 volts) on CKT 472 to the sensor. When the air is cold the sensor (thermistor) resistance is high, therefore the PCM terminal "PC9" voltage will be high. If the air is warm the sensor resistance is low, therefore the PCM terminal "PC9" voltage will be low.

DTC 23 Will Set When:
^ A signal voltage indicates an intake air temperature below about -40°C (-40°F).
^ Engine run time is greater than 320 seconds.
^ Vehicle speed is less than 15 mph.

Action Taken (PCM will default to): The Malfunction Indicator Lamp (MIL) will illuminate, the PCM will default to 60°C for intake air temperature (Tech 1 scan tool will not show defaulted value), and the cooling fan will enable.

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

1. This step checks if DTC 14 was set as a result of a hard or 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 sensor ground CKT 452 is open.

Diagnostic Aids: A Tech 1 scan tool displays temperature of the air entering the engine, which should be close to ambient air temperature when engine is cold, and rise as underhood temperature increases.

A faulty connection, or an open in CKT 472 or CKT 452 can result in a DTC 23.

If DTCs 23, 33 and 66 are stored at the same time, it could be the result of an open CKT 452. The "Temperature vs. Resistance Values" 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 can result in poor driveability.

Refer to "Intermittents," in "Diagnosis By Symptom." - Intermittent Malfunctions