Diagnostic Aids
WARNING: This page is about a different car, the 1994 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.
In areas in which the conditions cannot be easily maintained, especially in urban areas, it may be difficult to run the OBD-II status Code P0420 test. Use the following procedure to minimize the amount of driving required to complete test.
- Allow engine to warm completely.
- Place vehicle in Park. Using Tech 1, monitor mass airflow. Hold part throttle to maintain a reading of greater than 12 grams per second for at least 2 minutes. This will achieve the warm catalyst criteria for running test.
- Operate the vehicle in 2nd or 3rd gear to remain within conditions required to cause Code P0420 to set. If stopping is required, maintain warm catalyst criteria by placing vehicle in Park or Neutral and holding part throttle to maintain a mass airflow reading of greater than 12 grams per second for the duration of the stop.
- HO2S No. 2 Activity Test: Using a Tech 1, monitor mass airflow, HO2S No. 1 and HO2S No. 2 displays in Park while using Tech 1 IAC RPM control function to maintain a mass airflow of 10 grams per second (A/C off). Compare HO2S No. 1 and HO2S No. 2 activity (amplitude and frequency) to one another during a 30 second period. If HO2S No. 2 activity is nearly as great as HO2S No. 1 activity, a problem exists. Diagnosis using Code P0420 chart. If much less activity is noted, system is properly functioning.