Circuit Description

PCM reads Heated Oxygen Sensor (HO2S) activity for 90 seconds after closed loop operation has begun. During this period, PCM counts the number of Lean/Rich (L/R) and Rich/Lean (R/L) switches. With this information, an average time for all transitions can be determined. PCM then divides R/L average by L/R rich average to obtain a ratio. If HO2S ratio is not within range, DTC P1134 will set.

Conditions required to set DTC are:

• No ECT, IAT, MAF, MAP, or TP sensor DTCs set.
• No fuel trim, injector or HO2S heater circuit DTCs set.
• No EGR or EVAP system DTCs set.
• ECT is greater than 140°F (60°C).
• Engine speed is 1500-3500 RPM.
• Engine running at least two minutes.
• MAF calculated airflow is 17-32 grams/sec.
• Canister purge duty cycle is greater than 2 percent.
• Vehicle operating in closed loop mode.
• Listed conditions are present during 3-second monitoring period.
• About 90 seconds after closed loop, HO2S-1 transition ratio between lean-to-rich and rich-to-lean is less than .44 and greater than 3.8.