Hybrid Hardware and Monitor Operation

1. The hybrid vehicle exhaust system uses 2 separate HO2S. The front HO2S is the primary fuel control sensor. This sensor is the first HO2S in the exhaust stream and is referred to as the HO2S11. The last HO2S downstream in the exhaust system is used to monitor the catalyst and is referred to as HO2S12. For additional HO2S information, refer to the HEATED OXYGEN SENSOR (HO2S) MONITOR .

   The catalyst monitor uses an index ratio algorithm. This means in order to assess catalyst oxygen storage, the catalyst monitor counts precatalyst HO2S11 switches during part-throttle, closed loop fuel conditions after the engine is warmed up and the inferred catalyst temperature is within limits. The HO2S11 switches are accumulated in up to 3 different air mass regions or cells. While catalyst monitoring entry conditions are being met, the pre and post-catalyst HO2S signal lengths are continually being calculated. When the required number of precatalyst HO2S11 switches has accumulated in each cell, the total signal length of the post-catalyst HO2S12 is divided by the total signal length of the HO2S11 to compute a catalyst index ratio. An index ratio near 0.0 indicates high oxygen storage capacity, hence high HC efficiency. An index ratio near 1.0 indicates low oxygen storage capacity, hence low HC efficiency. If the actual index ratio exceeds the threshold index ratio, the catalyst is considered failed.

Typical Index Ratio Monitor Entry Conditions:

• Minimum 330 seconds since start-up at 21°C (70°F)
• Engine coolant temperature is between 76.6°C - 110°C (170°F - 230°F)
• Intake air temperature is between -7°C - 82°C (20°F - 180°F)
• Time since entering close loop is 30 seconds
• Inferred post-catalyst HO2S sensor temperature of 482°C (900°F)
• EGR is between 1% and 12%
• Part throttle, maximum rate of change 0.2 volts/0.05 sec
• Vehicle speed is between 8 and 112 km/h (5 and 70 mph)
• Fuel level greater than 15%
• First Air Flow Cell:
  • Engine RPM 1,000 to 1,300
  • Engine load 15% to 35%
  • Inferred catalyst temperature 454°C - 649°C (850°F - 1,200°F)
  • Number of front HO2S switches: 50
• Second Air Flow Cell:
  • Engine RPM 1,200 to 1,500
  • Engine load 20% to 35%
  • Inferred catalyst temperature 482°C - 677°C (900°F - 1,250°F)
  • Number of front HO2S switches: 70
• Third Air Flow Cell:
  • Engine RPM 1,300 to 1,600
  • Engine load 20% to 40%
  • Inferred catalyst temperature 510°C - 704°C (950°F - 1,300°F)
  • Number of front HO2S switches: 30
• The DTC associated with this test is P0420. Because an exponentially weighted moving average algorithm is used for concern determination, up to 6 drive cycles may be required to illuminate the MIL during normal driving. If the keep alive memory (KAM) is reset or the battery is disconnected, a concern illuminates the MIL in 2 drive cycles.