Oxygen Sensor
Some vehicles have (2) and some have (4) O2 sensors.
When you start looking at the O2 sensors, they are normally numbered something like "Bank 1 Sensor 1" Bank 1 is on the passenger side; Bank 2 is on the driver's side. Sensor 1 is the upstream sensor (near the frame, between the block and the cat) and Sensor 2 is near the Y-pipe (downstream of the cat).
Normally it is the upstream sensors (sensor 1) that go first. They see the harshest conditions.
You will need;
Oxygen Sensor Socket
Anti-Seized
Penetrating Oil
I have even used a small plumbers propane tank and heat it up and it help get them free.
Sometimes it will take 15 minutes or take a few hours it depends on your luck...
Bank 1 is the passenger side of the engine on your Ford Mustang Sensor 2 is in the exhaust after the catalytic converter ( downstream )
Bank 2 is the driver's side of the engine in your Ford Mustang Sensor 2 is in the exhaust after the catalytic converter ( downstream )
On a Ford Mustang ( V6 and V8 ) Bank 1 is the passenger side of the engine
bank 1 is the passenger side of the engine in your Ford Mustang , and sensor 2 is after the exhaust has passed through the catalytic converter ( downstream )
bank 2 is the drivers side of the engine in your Ford Mustang , and sensor 2 is after the exhaust has passed through the catalytic converter ( downstream )
Bank 1 is the passenger side of the engine in your 2000 Ford Mustang V6 Sensor 1 is before the catalytic converter ( upstream ) Sensor 2 is after the catalytic converter ( downstream )
Bank 2 is the drivers side of the engine in your Ford Mustang Sensor 1 would be near the motor before the exhaust enters the catalytic converter
Bank 2 is the drivers side of your Mustang engine Sensor 2 would be after the catalytic converter ( downstream )
On a Ford Mustang ( V6 and V8 ) Bank 1 is the passenger side of the engine
Bank 2 is the drivers side of your Ford Mustang engine Sensor 1 would be between the motor and the catalytic converter ( upstream )
Bank 2 is the drivers side of your Ford Mustang engine Sensor 1 is somewhere between the engine and the catalytic converter
On a 2001 Ford Mustang , 3.8 liter V6 engine : Bank 1 is the passenger side of the engine Sensor 1 would be close to the engine BEFORE the exhaust enters the catalytic converter