Federal Emissions

Code 23 Diagnostic Chart:

Intake Air Temperature (IAT) Sensor Circuit Diagram:

CIRCUIT DESCRIPTION
The Intake Air Temperature (IAT) sensor uses a thermistor to control the signal voltage to the 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 will see a high signal voltage. If the air is warm the sensor resistance is low, therefore, the ECM will see a low voltage.

The IAT sensor is located in the air cleaner.

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. DTC 23 will set if:
^ A signal voltage indicates an Intake Air Temperature (IAT) below -35°C (-31°F).
^ Time since engine start is 4 minutes or longer.
^ Vehicle speed less than 1 mph.
^ Start-up engine coolant temperature is less than or equal to -35.5°C (31.9°F).
^ All conditions met for 10 seconds.

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 5 volts return CKT 802 is open.

DIAGNOSTIC AIDS:

^ A Tech 1 (or equivalent) scan tool reads the temperature of the air entering the engine and should read close to ambient air temperature when the engine is cold and rises as underhood temperature increases.

^ A faulty connection or an open in CKT 472 or CKT 802 will result in a DTC 23.

^ DTCs 23 and 34 stored at the same time could be the result of an open CKT 802, which would also turn the temperature warning indicator "ON." CKT 802 is routed through a mini harness. 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.