Failure Conditions

Catalytic converter efficiency is determined by comparing front and rear HO2S signals. ECM will set a DTC and illuminate MIL if front and rear HO2S signals are similar more than 60 percent of the time during 2 of 4, 170-second monitoring periods during 2 drive cycles. ECM measure HO2S output signals when the following conditions are met:

• ECM is operating in closed loop.
• Engine speed is 1800-3200 RPM.
• Catalytic converter temperature is more than 702°F (372°C).
• Fuel vapor canister purge function is more than 0.9.
• Vehicle is not shifting gears.
• Engine load time is 1.4-4.5 mS.

This DTC indicates that catalytic converter has been found to have a low efficiency according to the readings of front and rear HO2S.