GM Service Manual Online
For 1990-2009 cars only

Description

The purpose of this test is to satisfy the enable criteria necessary to execute inspection/maintenance (I/M) readiness diagnostics for the heated oxygen sensor (HO2S) system. The test may be used to set the I/M System Status to YES.

Conditions for Running

    • The start-up engine coolant temperature (ECT) is less than 50°C (122°F).
    • The start-up intake air temperature (IAT) is less than 50°C (122°F).
    • The difference between the IAT and the ECT is less than 8°C (14°F).
    • The battery voltage is between 11-18 volts.

Diagnostic Aids

The HO2S Heater Tests will normally run within the 2 minutes allotted in the procedure. If there is an indeterminate condition, the test may take up to 8 minutes on some vehicles before a decision of pass or fail is made. If the test does not update within the allotted period of time, continue operation within the enable conditions until the test updates to YES. If the test does not update to YES, it may have failed or aborted due to the loss of enabling conditions. Extremely high ambient temperatures may prevent the HO2S Heater Test from initiating.

The I/M System Status does not indicate whether the test has passed or failed, only that a decision was made. When all of the diagnostics for a specific system have run and passed, the I/M System Status will update to YES. If a test for a specific system has failed, the I/M System Status will update to YES, indicating a determination was made, even if all of the required tests have not run. When a failure occurs, the Emission Related DTC portion of the I/M System Status display will indicate the malfunction indicator lamp (MIL) is requested. The I/M System Status also registers the number of diagnostic trouble codes (DTCs).

The first failure of a type B DTC does not constitute a final determination of pass or fail, and will not update the I/M System Status to YES. A second trip is required, and all the conditions to run must be met in order for the test to run again. These conditions may include a partial to complete engine cool down.

The I/M System Status will update only when an emission related DTC fails the second time, or when all of the tests pass.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load, such as a cooling fan or an A/C compressor clutch turning ON, may cause the test to abort.

If a diagnostic test is difficult to run, maintain necessary enable conditions until the system status updates to YES.

Step

Action

Value(s)

Yes

No

1

Did you perform the Inspection/Maintenance (I/M) System Check?

--

Go to Step 2

Go to Inspection/Maintenance (I/M) System Check

2

    Important: Whenever the ignition is turned ON, ignition positive voltage is supplied to the heated oxygen sensor (HO2S) heaters. After verifying the enable criteria, turn OFF the ignition for approximately 5 minutes to allow the sensors to cool before continuing with the test.

  1. Preprogram the scan tool with the vehicle information before the ignition is turned ON.
  2. Ensure that the vehicle is within the Conditions for Running specified in the supporting text.
  3. Set the vehicle parking brake.
  4. Verify that the transmission is in Park for automatic transmissions and Neutral for manual transmissions.
  5. Turn OFF all of the accessories, e.g., A/C, blower fan, etc.
  6. Start the engine and allow the engine to idle.
  7. Allow the engine to idle for the specified time or until the I/M System Status indicator updates to YES.

Did the HO2S Heater System Status update to YES?

2 minutes

Go to Step 5

Go to Step 3

3

Observe the DTC information, with a scan tool.

Does the scan tool indicate any failed DTCs?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 4

4

  1. Refer to Inspection/Maintenance (I/M) System DTC Table to determine which DTCs are required to run in order to complete this test.
  2. Observe the Not Ran Since Code Cleared display, with a scan tool.
  3. Determine which of the DTCs required for a YES status has not run.
  4. Enter the DTC number in the Specific DTC menu of the scan tool.
  5. Operate the vehicle within the Conditions for Running the DTC, located in the supporting text for the diagnostic table of the DTC.
  6. Repeat the procedure until the scan tool indicates the diagnostic test has run.
  7. Repeat steps 4-6 for any additional required DTCs that have not run.
  8. Observe the I/M System Status display, with a scan tool.

Did the HO2S Heater System Status update to YES?

--

Go to Step 5

Go to Diagnostic Aids

5

Observe the Emission Related DTC portion of the I/M System Status display, with a scan tool.

Does the scan tool indicate any Emission Related DTCs set?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK