Mysterious third 02 Sensor - I cannot find it.

[josephmartins]

I've seen references to a third 02 sensor, but I am hoping someone might have a picture of its location.

I replaced the sensor after the CAT as well as the sensor up at the top of the exhaust. Where is the one in between? I just jacked up the Avalon and followed the exhaust several times from the first sensor along the pipes to the rear sensor and I do not see a third sensor anywhere in between. If you happen to have a photo of its location or can describe to me how to locate it, I'd really appreciate the help. Thanks in advance.

[KoG506]

Originally Posted by josephmartins

I've seen references to a third 02 sensor, but I am hoping someone might have a picture of its location.

I replaced the sensor after the CAT as well as the sensor up at the top of the exhaust. Where is the one in between? I just jacked up the Avalon and followed the exhaust several times from the first sensor along the pipes to the rear sensor and I do not see a third sensor anywhere in between. If you happen to have a photo of its location or can describe to me how to locate it, I'd really appreciate the help. Thanks in advance.

So there is one on the front exhaust manifold. 2nd is the one after the CAT/exhaust pipe(under car) and 3 is behind the engine block. below the rear spark plugs

[josephmartins]

KoG506, does the one behind the block enter the exhaust from directly above? I assume it's tucked up in there because I missed it each time I looked. I'll have to put the Avalon up on ramps and have another look. Thanks for the response.

[bobflood]

Originally Posted by KoG506

So there is one on the front exhaust manifold. 2nd is the one after the CAT/exhaust pipe(under car) and 3 is behind the engine block. below the rear spark plugs

Just to be technically correct: There are two "Sensor 1s" - one for each bank of cylinders before the catalytic converter. The one for "bank 2" is at the front of the engine bay; the one for "bank 1" is at the rear of the engine bay; each is in its respective exhaust manifold ahead of the cat. The Bank 1 Sensor 1 is hard to see, as the exhaust manifold is right up close to the firewall. The rear sensor, behind the cat, is usually identified as "Bank 1, Sensor 2" even though it technically serves both banks. Sensor 1 is called an "Air/Fuel Sensor" instead of an O2 Sensor (also sometimes called a 'Wideband O2 Sensor") but it does the same thing.

[josephmartins]

Thank you for the clarification Bob, I appreciate it. I finally found B1S1 hiding up in the back of the bay. I haven't touched the sensor yet, but seeing that tight space reminds me of the seemingly impossible lower center bolts on a Jeep 4.0L exhaust manifold. Hoping I can get up in there at the right angle with the Avalon up on ramps. Fun fun.

[avalonshoe]

pics here

Where is Bank 1 Sensor 1

[bobflood]

Originally Posted by avalonshoe

pics here

Where is Bank 1 Sensor 1

These pics are WRONG!!! Bank 1 and Bank 2 labels are switched, there are 4 sensors instead of three, and they show 8 cylinder manifolds!! In the Avalon, Bank 1 is at the rear of the engine compartment and Bank 2 is at the front; there is a "sensor 1" in each bank before the cat and a single "sensor 2" after the cat; and we only have 6 cylinders.

[avalonshoe]

My bad, it should be this-->




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