Powertrain Controls - ECM/PCM

DTC 23 Chart Intake Air Temperature Sensor Circuit:

Intake Air Temperature Sensor Wiring 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.

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

1. DTC 23 will set if:

^ Temperature below -38°C (-36°F).
^ Engine coolant temperature above 29°C (85°F).
^ Engine idling (0% throttle).
^ No VSS (vehicle not moving).
^ All conditions met for 60 seconds.

OR

^ A signal voltage indicates an intake air temperature below -38°C (-36°F).
^ DTC 14 or 15 present.
^ Engine run time greater than 60 seconds.
^ Engine idling (0% throttle).
^ No VSS (vehicle not moving).
^ All conditions met for 12 seconds.

2. A DTC 23 will set, due to an open sensor, wire, or connection. This test simulates a DTC 25. If the ECM recognizes the high signal voltage, (high temperature) and the scanner displays 130°C (266°F) or above, the ECM and wiring are OK.

3. This will determine if the IAT sensor signal (CKT 472) or the IAT sensor ground (CKT 808) is open.

Diagnostic Aids:

^ Scan tool displays temperature of the air entering the engine and should be close to ambient air temperature when engine is cold, and rises as underhood temperature increases.

^ Carefully check harness and connections for possible open. - Intermittent Malfunctions

^ 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.