GM Service Manual Online
For 1990-2009 cars only

Description

The purpose of this test is to satisfy the enable criteria necessary in order to execute the 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. Ensure the vehicle meets the requirements listed in Conditions for Running before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

Conditions for Running

    • The startup engine coolant temperature (ECT) is less than 50°C (122°F).
    • The startup 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 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 MIL is requested. The I/M System Status also registers the number of 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 the DTC fails the second time, or 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 review 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 the 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, observe the I/M System Status display while maintaining the necessary enable conditions until the system status updates to YES.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.

  2. Preprogramming the scan tool will reduce the amount of time the oxygen sensor heaters operate while verifying the enable criteria.

  3. This step is to identify a first failure of a type B DTC. A DTC only appears on the I/M System Status display when it becomes a MIL-illuminating DTC. This occurs on the second failure of a type B DTC. A first failure of a type B DTC will not allow the I/M System Status to update to YES. Refer to Diagnostic Aids.

  4. This step is to help to identify any unique or unusual criteria that are required to run the diagnostic test if the universal set procedure does not. This information is in the service information under Conditions for Running the DTC.

  5. The I/M System Status only reports on whether or not a diagnostic has run, not the outcome of the test. If any emission-related DTC sets after the tests are complete, the DTC will require diagnosis.

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 HO2S heaters. After verifying the enable criteria, turn OFF the ignition for approximately 5 minutes in order 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 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 in Neutral for manual transmissions.
  5. Turn OFF all of the accessories, including the A/C and the blower fan
  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

With a scan tool, observe the DTC information.

Does the scan tool indicate any failed DTCs?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 4

4

  1. Refer to Inspection/Maintenance (I/M) System DTC Table in order to determine which DTCs are required to run in order to complete this test.
  2. With a scan tool, observe the Not Ran Since Code Cleared display.
  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. With a scan tool, observe the I/M System Status display.

Did the HO2S Heater System Status update to YES?

--

Go to Step 5

Go to Diagnostic Aids

5

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

Does the scan tool indicate any Emission Related DTCs set?

--

Go to Diagnostic Trouble Code (DTC) List

System OK