Need to know were the bank one , sencer one is on my buick century 2000 v6

Oxygen sensors are always numbered like this:
Bank 1 sensor 1
Bank 2 sensor 1
Bank 1 sensor 2
Bank 2 sensor 2

Some manufacturers use a kind of shorthand that reads different, but means the same thing:
Sensor 1/1 or O2s 1/1
Sensor 2/1 or O2s 2/1
Sensor 1/2 or O2s 1/2
Sensor 2/2 or O2s 2/2

Bank 1 is always the side of the engine where cylinder number 1 is located and, of coarse, Bank 2 is the opposite side.
On a 4 cylinder engine, there is only 1 bank and it is always referred to as Bank 1.

Sensor 1 is always the upstream sensor (The one located BEFORE the catalytic converter)
Sensor 2 is always the downstream sensor (the one that is located AFTER the catalytic converter.

Hope helps (remember to rate this).

Bank one is always on the same side of the engine as the number one cylinder. In your case the backside near the firewall. Bank 2 is the other side.

Sensor one always refer to the sensor before the catalytic converter. Sensor 2 is always after the catalytic converter.

So Bank 1 Sensor 1 will be in the exhaust manifold on the back side of the engine (firewall side) and before the catalytic converter. I should be mounted in the exhaust manifold dead center

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