Powertrain Controls - ECM/PCM

Diagnostic Trouble Code 23:

Intake Air Temperature Sensor Circuit:

CIRCUIT DESCRIPTION
The Intake Air Temperature (IAT) sensor uses a thermistor to control the signal voltage to the Engine Control Module (ECM). The ECM applies a voltage (about 5 volts) on CKT 472 to the sensor. When the intake air is cold, the sensor (thermistor) resistance is high, therefore, the ECM will sense a high signal voltage. If the intake air is warm, the sensor (thermistor) resistance is low, therefore, the ECM will sense a low signal voltage.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. Diagnostic Trouble Code (DTC) 23 will set if:

^ Time since engine start is longer than 5 minutes.
^ Vehicle speed is less than 44 mph.
^ IAT sensor signal voltage indicates a temperature below -28°C (-20°F) for 5 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 IAT sensor signal (CKT 472) or the IAT sensor ground (CKT 455) is open.

DIAGNOSTIC AIDS
IAT on a scan tool indicates the temperature of the air in the air cleaner.

Carefully check harness and connections for possible open CKT 472 or CKT 455.

If DTC 33 also is set, check CKT 455 for an open or poor connection.

If the engine has been allowed to sit overnight, the intake air temperature and engine coolant temperature values should be within a few degrees of each other. After the engine is started, the IAT will increase due to thermostatic air cleaner operation and underhood temperatures.

Refer to Intermittents in Diagnosis By Symptom. - Intermittent Malfunctions