For 1990-2009 cars

### Description

The purpose of this test is to satisfy the enable criteria necessary to execute 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 engine is running.

• | The battery voltage is between 10.5-16 volts.

• | The test will always initiate after a cold start. The control module considers the engine to be cold if the engine coolant temperature (ECT) is below 24°C (75°F).

### 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 from initiating. The oxygen sensor heaters are operated by the engine control module. The control module has the ability to monitor the current required by the heaters and does this on a continuous basis.

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.

### Test Description

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

1. Make sure you 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. The HO2S Heater Tests may not complete when initiated from a cold start and may require running under a load in order to complete the tests.

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 the DTC t 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 identify any unique or unusual criteria required to run the diagnostic test in the event 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 what the outcome of the test was. 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: Once the engine is started, DO NOT turn OFF the engine for the remainder of the procedure until the test is complete.

1. Start and idle the engine.
2. Ensure the vehicle is within the Conditions for Running specified in the supporting text.
3. Set the vehicle parking brake.
4. Verify 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 and idle the engine.
7. Idle the engine until the engine reaches operating temperature of at least 70°C (158°F). This may be up to 8-10 minutes depending on the start up coolant temperature.

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 the remaining portion of this test to run, the vehicle must operate in the following conditions:

8. Acceleration at part throttle to 48-80 km/h (30-50 mph).
9. Speed maintained for 2 minutes 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 the Inspection/Maintenance (I/M) System DTC Table to determine which DTCs are required to run in order to complete this test.
2. Operate the vehicle within the Conditions for Running the DTC, located in the supporting text for the diagnostic table of the DTC.
3. Repeat the procedure until the scan tool indicates the diagnostic test has run.
4. 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