On the exhaust pipe, lower, possibly near the catalytic converter.
Look under the vehicle and count them.
On a 2000 Mercury Mountaineer ( 4.0 V6 and 5.0 V8 ) Bank 2 is the drivers side of the engine Sensor 1 is close to the engine BEFORE the exhaust enters the catalytic converter Sensor 2 is AFTER the exhaust has passed through the catalytic converter
Bank 2 is the drivers side of the engine in your Mercury Mountaineer Sensor 2 is in the exhaust after the catalytic converter
Bank 2 is the drivers side of the engine in a Mercury Mountaineer Sensor 2 is in the exhaust after the catalytic converter ( downstream )
Bank 2 is the drivers side of the engine in your Mercury Mountaineer Sensor 1 is between the engine and the catalytic converter ( upstream ) Sensor 2 is after the catalytic converter ( downstream )
On a 1997 Mercury Mountaineer ( V6 and V8 ) Bank 2 is the drivers side of the engine
Bank 2 is the drivers side of the engine in a 2002 Mercury Mountaineer Sensor 2 is after the catalytic converter ( downstream )
On a 2002 Mercury Mountaineer ( V6 and V8 engines ) Bank 2 is the drivers side of the engine Sensor 1 would be close to the engine BEFORE the exhaust enters the catalytic converter
It is after the last catalytic converter.
Bank 2 is the drivers side of the engine in your Mercury Mountaineer ( V6 + V8 ) Sensor 1 is in the exhaust close to the engine before the exhaust enters the catalytic converter
Bank 1 is the passenger side of the engine in a Mercury Mountaineer ( V6 + V8 ) Sensor 2 is after the catalytic converter ( downstream )