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O2 Sensor Identification and Locations

Which o2 sensor do I need?

In recent years we have seen a rapid increase of vehicles using multiple oxygen sensors, and also an increasing number utilising air/fuel ratio type sensors. Some of the very latest models also now incorporate a NOx sensor as well. Some vehicles can have 8 or more oxygen sensors fitted.

Oxygen sensors are located within the exhaust stream, there is at least one oxygen sensor located before the catalytic converter and typically one in each exhaust manifold. Depending on the exhaust system design there may be one or two located after the catalytic converter to monitor its effectiveness.

So which o2 sensor do you need? Identifiying the type and location of your oxygen sensor will ensure you replace your old sensor with the correct new oxygen sensor. Different sensor types are NOT interchageable and fitting a incorrect type may damage you vehicles computer (ECU)

If your vehicle has had a diagnostic test you may for example have a code displayed “sensor B1 S1 faulty”. So what does this mean, what is B1 or S1? Well what this is suggesting is that Bank 1 Sensor 1 is faulty.

So what is Bank 1?
Bank 1 is where the Number 1 cylinder is located. This is always the forward most cylinder.

Typical Engine Bank Identification

(Click to enlarge)

So what is Sensor 1?
Sensor 1 is the O2 sensor that is located before or upstream of the catalytic converter. (Pre-cat)

So then if your diagnostic code is B1 S2 that means Bank 1 Sensor 2 down stream (post-cat).
If its B2 S2 that means Bank 2 (opposite Bank to Bank 1) and the downstream after cat o2 sensor.


Oxygen Sensor Locations

Depending on the make, model and engine type of your vehicle oxygen sensors can be found in a variety of places.
In the diagrams below we have detailed some of the more common locations. Click on the image to enlarge.

Traditional V6 and V8

Traditional V6 and V8

4 and 6 Cylinders In-line


4 Cylinder Transverse



EGR Valves Ignition Leads