Powertrain Controls - ECM/PCM

Trouble Code 23 Chart:

Intake Air Temperature Sensor Wiring Schematic:

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: IAT signal indicates a temperature of -35°C (-31°F) or less for greater than 4 minutes.

Action Taken (PCM will default to): The PCM will IAT 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 469 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 469 will result in a DTC 23.
^ DTCs 23 and 34 stored at the same time could be the result of an open CKT 469. A faulty connection could result in intermittent failures. The "Temperature to Resistance Values" scale in the chart 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 in "Diagnosis by Symptoms". Testing and Inspection