The scan tool displays 0.0-25.5. The Air Fuel Ratio (A/F) indicates the PCM commanded value. In closed loop, A/F should normally be around 14.2-14.7. A lower A/F indicates a richer commanded mixture, which may be seen during Power Enrichment or Three-Way Converter (TWC) Protection modes. A higher A/F indicates a leaner commanded mixture. This can be seen during Decel Fuel Mode.