Powertrain Controls - ECM/PCM

DTC 23 Chart:

Intake Air Temperature Sensor Circuit:

Circuit Description:
The Intake Air Temperature (IAT) sensor is a thermistor that controls a signal voltage to the PCM. The PCM applies approximately 5 volts to the sensor on CKT 472. When the intake air is cold, the sensor resistance is high, therefore the voltage sensed at the input "C29" is high. If the air is warm, the sensor resistance will be low, and the voltage input to the PCM will be low.

DTC 23 Will Set When:
A signal voltage indicates an IAT less than -35.5°C (-35.9°F), a signal voltage indicates that engine coolant temperature is greater than -35.5°C (-31.9°F), time since engine start is 4 minutes or longer, vehicle speed is less than 1 mph with all conditions met for 25 seconds.

Action Taken (PCM will default to):
The PCM will use an IAT default value of 37°C (108°F) and the MIL will become illuminated.

DTC 23 Will Clear When:
A current DTC 23 will clear when the intake air temperature is indicated above the DTC 23 threshold. A history DTC 23 will clear after 50 consecutive ignition key cycles without a current DTC 23 being stored.

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

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

2. This will determine if the signal CKT 472 or the 5 volts return CKT 802 is open.

Diagnostic Aids:
A Tech 1 scan tool reads the temperature of the air entering the engine, and should read close to ambient air temperature when the engine is cold. IAT values will rise as underhood temperature increases.

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

DTCs 23 and 34 stored at the same time could be the result of an open CKT 452. A faulty connection could result in intermittent failures. The "Temperature to Resistance Values" scale at the right may be used to test the IAT sensor at various temperature levels to evaluate the possibility of a "shifted" (mis-scaled) sensor. A "skewed" sensor could result in poor driveability complaints.

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