A/F vs O2 sensor - Denso website

[MaximaGuy]

Ordering O2 for my Highlander and the Densoautoparts.com has 2 sets

upstream called A/F and downstream called O2. Never knew they were called such, always thought they were O2s.

Anyway, would replacing the upstream be fine or would replacing all be needed.

 

[spasm3]

I just replace my upstream at around 80-100k. Never had a downstream one go bad.

 

[oilpsi2high]

It's possible the upstream sensor is a wideband.

Is the code for the upstream or downstream?

 

[MaximaGuy]

No codes but then with 190K the OEM served me very very well and intend to keep this going for at-least 50K miles.

 

[oilpsi2high]

If it's preventive maintenance then just replace the upstream. The car only uses the downstream for cat efficiency and generally doesn't affect how the car runs.

Where are you ordering from? I had to order FOUR for my truck and found a guy on eBay who has a surplus of o2's. I can see if he has yours in his store.

 

[bdcardinal]

Ford calls the front ones EGOs and HEGOs. The rear sensors are referred to as "cat monitors" since that is pretty much all they do.

 

[oilpsi2high]

If you have the 3.3 V6 here's the Denso sensor, it's about 50% cheaper than on RockAuto:

2349042 Oxygen Sensor Denso Highlander Toyota Lexus

 

[MaximaGuy]

https://www.densoproducts.com

 

[CharBaby]

On a Highlander/Lexus RX:
The upstream are the A/F sensors in the exhaust manifolds in either Bank 1 or Bank 2...each bank having it's own Cat. Conv.
The downstream is the single O2 sensor near the single Cat Conv/Resinator area.

 

[Virtus_Probi]

Originally Posted by bdcardinal
Ford calls the front ones EGOs and HEGOs. The rear sensors are referred to as "cat monitors" since that is pretty much all they do.

I remember the term UEGO from the automotive electronic design days, did those fail to catch on?

 

[MaximaGuy]

Folks, can someone help me with a picture on the upstream A/F sensors.
Have a CA vehicle and it has 4 sensors unlike the rest of the country and lost now.

 

[The Critic]

There are two upstream sensors and they are air/fuel (wideband) sensors. They are the same part number - #234-9042.

I am not sure why you are purchasing them from that site. Rockauto is significantly cheaper.

 

[mclasser]

I had to replace the A/F sensor on my Accord and it was considerably more expensive than a regular O2 sensor.

 

[MaximaGuy]

Went under to find the rear bank A/F, it right up there parallel to the one next to the radiator. Right up there under the throttle body.
Why would any moron put it right up there when there is a jungle of things next to the TB. Unbelievebly hard to get to the rear upstream ones.

 

[The Critic]

Originally Posted by MaximaGuy
Went under to find the rear bank A/F, it right up there parallel to the one next to the radiator. Right up there under the throttle body.
Why would any moron put it right up there when there is a jungle of things next to the TB. Unbelievebly hard to get to the rear upstream ones.

The sensor is the easy part. The connector is the hardest part.

I have done a few of the 3.0/3.3 sensors. They suck but are not terrible to do.

 

[MaximaGuy]

I had my daughter help me remove the connector although getting to the sensor has been tough.
A video on YouTube talks about going from under but then going from the passenger side (w/ wheel removed) with a long extension and flex head ratchet would seem easier.

Any ideas as to how its best to get to the sensor would be appreciated.

 

[Supersonic]

Can't be of much help but spray with penetrate and have both the socket and the crows-foot options available for removal. I've done it on my 3.5 2010 Sienna, but I don't know how similar it would be to the 2006 3.3. You might wanna go from above and take off the intake manifold, I did it while doing the plugs as preventative maintenance.

 

[MaximaGuy]

Originally Posted by Supersonic
Can't be of much help but spray with penetrate and have both the socket and the crows-foot options available for removal. I've done it on my 3.5 2010 Sienna, but I don't know how similar it would be to the 2006 3.3. You might wanna go from above and take off the intake manifold, I did it while doing the plugs as preventative maintenance.


Got them replaced but the rear sensor is no walk in the park - one needs long pliers and tons of patience. Doing this when replacing the plugs is the best PM and its easy but with the intake its is a nightmare. One other PM would be when changing the plugs at 120K/10yr is to replace the high-pressure power steering hose as well. They do leak w/o a fail on all models after 10-12 yrs.