GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Epica 🢒 DTC 🢒 DTC 025

Circuit Description

The intake air temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. The engine control module (ECM) applies 5 volts through a pull-up resistor to the IAT sensor. When the temperature is cold, the IAT sensor resistance is high and the ECM will monitor a high signal voltage on the IAT circuit. If the intake air is warm, the sensor resistance is lower, causing the ECM to monitor a lower voltage.

Conditions for Setting the DTC
    • The engine has been running longer than 120 seconds.
    • The IAT sensor signal voltage indicates a temperature less than -35°C (-31°F).

Diagnostic Aids

Inspect the wiring harness for damage. If the harness appears to be OK, observe the IAT sensor display on the scan tool while moving the connectors and the wiring harnesses related to the IAT sensor. A change in the display will indicate the location of the fault.

Step

Action

Values

Yes

No

1

Was the Diagnostic System Check-Engine Controls performed?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2
  1. Connect the scan tool to the data link connector (DLC).
  2. Run the engine until it reaches operating temperature.

Does the scan tool show the intake air temperature (IAT) sensor reading within the specified range?

10-80°C (50-176°F)

Go to Diagnostic Aids

Go to Step 3

3
  1. Turn the ignition to LOCK.
  2. Disconnect the IAT sensor connector.
  3. Jumper the IAT connector terminals.
  4. Turn the ignition ON.

Does the scan tool show the IAT sensor reading above the specified value?

180°C (356°F)

Go to Step 4

Go to Step 5

4

Inspect for a faulty connector or terminals at the IAT sensor connector.

Is the condition found?

--

Go to Step 10

Go to Step 9

5

Measure the voltage between terminals 1 and 2 of the IAT connector.

Does the voltage measure within the specified range?

4.5-5.5 V

Go to Step 11

Go to Step 6

6

Measure the voltage between the IAT terminal 2 and the battery ground, negative, post.

Does the voltage measure within the specified range?

4.5-5.5 V

Go to Step 7

Go to Step 8

7
  1. Turn the ignition to LOCK.
  2. Inspect for an open or short to battery voltage in the wire between the IAT connector terminal 2 and the engine control module (ECM) connector terminal D15.

Is the condition found?

--

Go to Step 10

Go to Step 11

8
  1. Turn the ignition to LOCK.
  2. Inspect for an open or short to battery voltage in the wire between the IAT connector terminal 1 and the ECM connector terminal B4.

Is the condition found?

--

Go to Step 10

Go to Step 11

9
  1. Turn the ignition to LOCK.
  2. Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement .
  3. Clear any DTCs from the ECM.
  4. Run the engine until it reaches operating temperature.
  5. Perform the Diagnostic System Check-Engine Controls.

Is the replacement complete?

--

System OK

--

10
  1. Turn the ignition to LOCK.
  2. Repair the wire or the connector terminal as needed.
  3. Clear any DTCs from the ECM.
  4. Run the engine until it reaches operating temperature.
  5. Perform the Diagnostic System Check-Engine Controls.

Is the repair complete?

--

System OK

--

11
  1. Replace the ECM. Refer to Engine Control Module Replacement .
  2. Run the vehicle until it reaches operating temperature.
  3. Perform the Diagnostic System Check-Engine Controls.

Is the replacement complete?

--

System OK

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