GM Service Manual Online
For 1990-2009 cars only

Description

The purpose of this test is to satisfy the enable criteria that are necessary in order to execute I/M readiness diagnostics for the oxygen sensor (O2S, HO2S) system. The test can be used to set the I/M System Status to YES. Ensure that the vehicle meets the requirements listed in Conditions for Running before performing this test. Failure to meet the necessary requirements can produce inaccurate test results.

Conditions for Running

    • The engine coolant temperature (ECT) is more than 80°C (176°F).
    • The engine is running in Closed Loop fuel control.
    • The engine has been running for more than 4 minutes.
    • The battery voltage is between 11.7-16 volts.

Diagnostic Aids

If the status does not update, the test outlined in this procedure can be repeated until the I/M System Status updates to YES.

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 updates to YES. If a test for a specific system has failed, the I/M System Status updates 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 indicates 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 updates 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 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. You must perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.

  2. The oxygen sensor tests begin shortly after the indicated speed is achieved. The engine RPM may be too low in overdrive on manual transmission vehicles. If difficulty is encountered updating the status, operate the vehicle in the recommended gear during the test. Chevrolet Metro, Prizm, and Tracker vehicles begin the oxygen sensor tests during the idle period immediately following the cruise period.

  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 malfunction indicator lamp (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 identify any unique or unusual criteria that are required to run the diagnostic test if the universal set procedure does not. This information is located 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

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

  1. Ensure that the vehicle is operating within the Conditions for Running specified in the supporting text.
  2. Turn OFF all of the accessories, including the A/C and the blower fan.
  3. Start the engine and allow the engine to idle.
  4. Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

    Important:  In order for this test to run, the vehicle must operate in the following conditions:

  5. Acceleration at part throttle to 75-90 km/h (45-55 mph), with this speed maintained for 6 minutes or until the I/M System Status updates to YES.
  6. Manual transmissions, either 5 or 6 speed, may require operation in 4th or 5th gear respectively, in order for this test to run.

    After the specified time has elapsed, Chevrolet Metro, Prizm, and Tracker vehicles require the following additional steps:

    4.1. Deceleration to 0 km/h (0 mph)
    4.2. Engine idling for 2 minutes
  7. With a scan tool, review the I/M System Status display.

Did the HO2S/O2S System Status update to YES?

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 the Inspection/Maintenance (I/M) System DTC Table 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/O2S 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