Powertrain Controls - ECM/PCM

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

Intake Air Temp Sensor Wiring Circuit:

Circuit Description:

The Intake Air Temperature (IAT) sensor uses a thermistor to control the signal voltage at the Engine Control Module (ECM). The ECM 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 ECM terminal "PC9" voltage will be high. If the air is warm the sensor resistance is low, therefore the ECM terminal "PC9" voltage will be low.

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

1. DTC 23 will set if:
^ A signal voltage indicates a intake air temperature below about -40°C (-40°F).
^ Time since engine start is 320 seconds or longer.
^ Vehicle speed less than 15 mph.
2. A DTC 23 will set due to an open sensor, wire, or connection. This test will determine if the wiring and ECM are OK.
3. This will determine if the signal CKT 472 or the sensor ground CKT 469 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 469 can result in a DTC 23.

DTCs 23 and 34 stored at the same time, could be the result of an open CKT 469. 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 "skewed" (mis-scaled) sensor. A "skewed" sensor could result in poor driveability complaints.

- Intermittent Malfunctionsin "Diagnosis By Symptom".