California and some European models have oxygen sensor(s). The ECU is designed to read the Oxygen Sensor under certain conditions and temporarily change the air/fuel ratio. The closed loop circuit has a very limited operating range, which is only in effect while holding a steady speed. The Oxygen sensor(s) can be disconnected but this will trip the F.I. dash warning light. By installing the Oxygen Sensor eliminator, the closed loop system is disabled and the F.I. light functions correctly 

 

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