Circuit Description

PCM monitors Heated Oxygen Sensor (HO2S) activity for 90 seconds after closed loop operation has begun. PCM determines if front HO2S is functioning properly by counting number of HO2S-1 Lean/Rich (L/R) and Rich/Lean (R/L) switches. If PCM determines that front HO2S did not switch enough times, DTC 1133 is set.

Conditions required to set DTC are:

• ECT is greater than 140°F (60°C).
• Engine is operating in closed loop.
• Engine running at least 2 minutes.
• Canister purge duty cycle is greater than 2 percent.
• MAF calculated airflow is 17-32 grams/sec.
• Engine speed is 1500-3500 RPM.
• All conditions are present for one second.
• About 90 seconds after closed loop, PCM monitors oxygen sensor as it switches greater than and less than .45 volt. If less than 12 R/L and L/R switches are detected, DTC P1133 will be set.