Circuit Description

WARNING: This page is about a different car, the 2000 Isuzu Rodeo and 2000 Isuzu Amigo. However, it is still accessible from the selected car via links, so may be relevant.

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.