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There is one in the exhaust system before the catalytic converter and sometimes one after it.
On your 2003 Ford Ranger , 4.0 liter SOHC , V6 : Bank 1 is the passenger side of the engine Sensor 1 would be close to the engine BEFORE the exhaust enters the catalytic converter Sensor 2 would be AFTER the exhaust exits the catalytic converter
Bank 2 is the drivers side of a V6 engine in a Ford Ranger Sensor 1 would be somewhere in the exhaust before the exhaust enters the catalytic converter ( upstream sensor )
Bank 1 is the passenger side of the engine in your 3.0 liter Ford Ranger Sensor 1 ( upstream sensor ) is in the exhaust before it enters the catalytic converter ( either in the exhaust manifold or exhaust pipe )
On your V6 engine : Bank 1 is the passenger side of the engine Sensor 1 is in the exhaust pipe ( or exhaust manifold ) before the exhaust enters the catalytic converter ( upstream )
Bank 1 is the passenger side of your V6 in a Ford Ranger Sensor 1 is somewhere close to the engine before the exhaust enters the catalytic converter
It is right on top of the Catalytic Converter.
There should be 2 (upstream) O2 sensors (one for each bank of cylinders) before the catalytic converter and only one (downstream) O2 sensor after the catalytic converter. All 3 are threaded into the exhaust system.
Bank # 1 is the passenger side of the engine Bank # 1 , SENSOR # 1 , is close to the engine in the exhaust Bank # 1 , SENSOR # 2 , is in the exhaust after the catalytic converter ( downstream )
On a Ford Ranger ( V6 engine ) Bank 2 is the drivers side of the engine Sensor 1 would be close to the engine before the exhaust enters the catalytic converter
I don't know about the catalytic converter (typically Rangers -at least the 4.0L V6 has 2 catalytic converters). But for the rest of the exhaust system : with 2 prebend pipes, gaskets and the muffler, you are looking at anywhere from $ 361 to $ 457.00 as of Dec 15, 2011. - it also depends on the shop who does the work. Hope this helps.
On a 2000 Ford Ranger , 3.0 and 4.0 liter V6 engines : Bank 1 is the passenger side of the engine Sensor 1 is close to the engine before the exhaust enters the catalytic converter ( it might even be in the outlet of the exhaust manifold )