For 1990-2009 cars

### Description

The purpose of this procedure is to satisfy the enable criteria necessary to execute inspection/maintenance (I/M) readiness diagnostics for the heated oxygen sensor (HO2S) heater system. This procedure may be used to set the HO2S Heater I/M System Status display on the scan tool to YES. The HO2S Heater I/M System Status display indicates whether or not the control module has completed the readiness diagnostics. The readiness diagnostics complete when all DTCs comprising the diagnostics run and pass, or any DTC comprising the diagnostics illuminates the malfunction indicator lamp (MIL). Once the diagnostics complete, the HO2S Heater I/M System Status display will be updated to YES.

### Conditions for Running

• | The engine coolant temperature (ECT) is more than 70°C (158°F).

• | The battery voltage is between 10-18 volts.

### Diagnostic Aids

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the system set procedure. If DTCs do not run and no DTC is set, review the appropriated scan tool data list and service information. This will give an indication of why the DTCs do not run. Some diagnostics may abort due to changes in the conditions while the diagnostics are running. For example, changes in engine load such as a cooling fan or A/C compressor clutch turning ON, may cause the diagnostics to abort. If the HO2S Heater I/M System Status does not update to YES, the procedure can be repeated until a YES status is achieved.

Step | Action | Values | 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 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 allow the engine to idle for the specified time.
7. Observe the I/M System Status display with a scan tool.

Did the HO2S Heater System Status update to YES?

2 minutes

Go to Step 6

Go to Step 3

3 | Caution: Refer to Road Test Caution in the Preface section. Important: If the HO2S Heater I/M System Status updates to YES at any time during the drive procedure, disregard the remaining numbers in this step.

1. Accelerate at part throttle to 89 km/h (55 mph) with this speed maintained for the specified time.
2. Decelerate to 32 km/h (20 mph).
3. Accelerate at part throttle to 89 km/h (55 mph).
4. Observe the I/M System Status display with a scan tool.

Did the HO2S Heater System Status update to YES?

2 minutes

Go to Step 6

Go to Step 4

4 | 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 5
5 |

1. Refer to Inspection/Maintenance (I/M) System DTC Table to determine which DTCs are required to run in order to update the HO2S Heater I/M System Status to YES.
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 numbers 4-6 of this step for any additional required DTCs that have not run.
7. Observe the I/M System Status display with a scan tool.

Did the HO2S Heater System Status update to YES?

--

Go to Step 6

Go to Diagnostic Aids

6 | 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