GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The engine control module (ECM) uses an intake air heater (IAH) to warm the incoming air for proper cylinder combustion. The ECM grounds the control coil of the IAH relay to energize the heater during cold operation. If the ECM detects voltage on the IAH circuit when the relay is commanded OFF, or incorrect voltage when the relay is commanded ON, a DTC will set.

Conditions for Running the DTC

    • The battery voltage is between 10-18 volts.
    • The intake air temperature (IAT) is less than 23°C (73°F) with the engine running.
        OR
    • The coolant temperature is less than 49°C (121°F) with the ignition ON, engine OFF for more than 3 seconds.

Conditions for Setting the DTC

The heater line voltage is more than 8.1 volts with the relay OFF.

OR

The heater line voltage is between 3.8-8.1 volts with the ignition OFF.

AND

The heater line voltage is less than 0.5 volt below battery voltage with the ignition ON.

OR

The heater line voltage is less than 3.8 volts with the relay OFF.

AND

The reference line voltage is low with the relay OFF.

Action Taken When the DTC Sets

    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Test Description

The number below refers to the step number on the diagnostic table.

  1. This step checks for battery voltage output from the IAH relay to the IAH.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Is DTC P0380 also set?

--

Go to DTC P0380

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Turn ON the ignition, with the engine OFF.
  3. Command the IAH ON and OFF with the scan tool.
  4. Observe the IAH parameter with the scan tool.

Does the scan tool display a voltage near the first specified value with the IAH commanded ON and near the second specified value with the IAH commanded OFF?

11-13 V, 0.0 V

Go to Step 9

Go to Step 4

4

  1. Turn ON the ignition, with the engine OFF.
  2. Touch the supply stud of the IAH with a test lamp connected to a good ground. Refer to Troubleshooting with a Test Lamp in Wiring Systems.
  3. Command the IAH ON and OFF with the scan tool.

Does the test lamp illuminate with the IAH commanded ON, and turn OFF with the IAH commanded OFF?

--

Go to Step 9

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Disconnect the IAH relay connector. Refer to Intake Air Heater Relay Replacement .
  3. Turn ON the ignition, with the engine OFF
  4. Probe the IAH relay harness connector ignition 1 voltage circuit with a test lamp connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 6

Go to Step 10

6

  1. Verify that the IAH relay harness is disconnected.
  2. Turn ON the ignition, with the engine OFF.
  3. Probe the IAH control circuit of the harness connector with a test lamp connected to battery voltage.
  4. Command the IAH ON and OFF with the scan tool.

Does the test lamp illuminate with the IAH commanded ON, and turn OFF with the IAH commanded OFF?

--

Go to Step 11

Go to Step 7

7

  1. Verify that the IAH relay harness is disconnected.
  2. Turn ON the ignition, with the engine OFF.
  3. Probe the IAH control circuit with a DMM connected to ground.

Does the voltage measure less than the specified value?

1 V

Go to Step 8

Go to Step 13

8

Test the IAH control circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 14

9

Test for an open or short to ground on one of IAH supply voltage circuits between the IAH supply stud and the ECM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 14

10

Repair the open or short to ground in the IAH ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 16

--

11

Test for poor connections at the IAH relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 12

12

Replace the intake air heater relay. Refer to Intake Air Heater Relay Replacement .

Did you complete the replacement?

--

Go to Step 16

--

13

Repair the short to voltage on the relay control circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 16

--

14

Test for poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 15

15

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement

--

Go to Step 16

--

16

  1. Use a scan tool to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 17

Go to Step 2

17

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK