I wish there was a common lingo for sensor location. I had a check light come on, and Autozone says its S1B1 (sensor1 Bank1), got that! But I go to buy one (I like Sparkplugs.com), and they are called "front" and "rear". Now I understand there are 3 in an Avalon, I can only assume "1" is in front, so I bought a "front" one (234-4622). I also hear that "1" is on the side of cylinder "1"... I can't find a number on the engine... and I read many conflicting messages about drivers side and passenger side.... well the exhaust on the Avalon goes down the center...

I had the same exact thing happen to my Tundra, except it was S2B2, I assumed that was "rear", replaced one of the two, and my 1st guess was right. Just not sure which is "front" on the Avalon, I read one post saying S1B1 was the "middle" one... please HELP, I'd like to guess right again.

This is the 2nd one in 30K miles (first was warrantee). Had 3 replaced on my Tundra in 35K miles. Wish there was a way to fool the car into thinking they all worked!

You didn't state which year Avalon you had...so I can only give you advice on what my 2001 model has.

On the '01, there is one O2 sensor and two A/F sensors. S1B1 refers to an A/F sensor as shown in this diagram:
http://files.automotiveforums.com/gallery/showphoto.php?photo=34392&password=&sort=1&cat=500&page=1

Hope that helps.

It's a 1999, V6, I think they are close to the same. So and "A/F" is a different part than an 02? Autozone said it was an 02 S1B1....

S1B1 is a A/F (you can see it on the link I posted). They're similar to an O2, but a few more $$ :rolleyes: from what I understand.

I believe the A/F's will show up on an OBDII scanner as an O2 sensor. It just reads the codes and that code is for O2.

Thanks for the quick response! After seeing the price of an A/F sensor (2.5X) I called Denso to confirm. Actually, they said only CA vehicles have the A/F sensors, mine (Texas) has all O2 sensors... The two "front" ones are the same, and could be either one, "S1B1" sometimes goes either way. Guess I'll replace the easiest one 1st, and see what happens....

I think Denso may have misled you. The 2001 Avalon uses A/F sensors up front and one O2 sensor after the cat. Maybe they just consider them "wide-band" O2 sensors vs the "narrow-band" sensor that sits behind the cat. Here's a link to an article on these that explains some of this:

http://www.autoshop101.com/forms/h37.pdf

You can buy the A/F sensors for $244 each (oxygensensors.com), but you're right--they're about 2.5x the cost of the O2 sensor. Walker sells a slightly cheaper version that will save you about $100, but the Denso is OEM.

Also, look again at the diagram of the sensors. S1B1 refers to a specific sensor, not "one of the two". That's the one you want to replace (though if you're replacing one of the A/F sensors, you should do it as a pair).

Guess I'll pull it and see what number is on it... the Denso guy did give me the part number of the cheaper "02 sensor", and said that only the CA cars in 1999 had the high dollar ones. He could be wrong... will let you know (if I can crawl under there and get to it). Thanks for that link, great article!

PS: I just went to Oxygensensors.com and they said I need the same 02 sensor that Sparkplugs.com (and Denso) said I needed, a Denso 234-4622 ($90). I did a search on 2001 and it came up with the high dollar A/F sensor, so I guess in 1999 they were still using the cheap ones (that crap out).

Lucky you :iceslolan I just noticed that you have a '99 whereas I thought you had a 2001. In that case, yeah, it's an O2 sensor.

And it worked! I had it in getting fluids changed and noticed the S1B1 was in a VERY difficult place (farside of the engine right up against the firewall), so I had them change it ($39), well worth that labor!