H21 - Check For Source of Potential HO2S Contamination

- Investigate the following items as a potential source of HO2S contamination.
- Use of unapproved Silicon sealers.
- Fuel contaminated by silicon additives.
- Excessive oil burning (i.e. rings, valve seals and oil overfill).
- Glycol (antifreeze) leaking internally in the engine.
- Lead contaminated fuel.
- Use of unapproved cleaning agents.

- Are any of the above conditions present?

YES -- REPAIR source of contamination. REPLACE HO2S and oil/filter. COMPLETE PCM reset to clear DTCs. COMPLETE a HO2S monitor drive cycle.

NO -- Go to H22. H22 - Check For Unmetered Air Leaks>