2nd Gen Prius (2006) Upstream O2 Sensor / AF sensor replacement - EASY way

[@jamesmichaelfreer]

Just did mine! Thanks for the tool recommendation, got it from underneath too. I did take off the wiper assembly, not that difficult, other KZbin videos were helpful, made access to the “plug in connector easier”, I pushed the release tab,facing the front left tire, with the corner of a long screw driver, and simultaneously pulled, the connector was the most challenging, but doable!

[@SteveRabb-h4e]

Great info on the replacement and unique socket needed due to the sensor's heatshield. Arm is too fat to squeeze as you did, so had to get it from the top by removing all the wiper stuff. Too bad it wasn't the downstream (cost less and easy to access). Thanks for taking the time to put this out there.

[@xj1223]

Thank you, thank you for the Schley tool recommendation. I went in through the bottom but didn't remove anything because I have a catalytic shield in place. I was lucky enough to have access to a grease pit under the car where I could stand up while working underneath. The actual removal of the sensor from the exhaust took about 15 minutes, with most of that time trying to wiggle the tool and ratchet into place. HOWEVER I got stuck on disconnecting the wire plug from it's connection socket. I first tried your method of going in from the top, as my arm was thin enough. But after 45 minutes of trying to wiggle off the socket, I removed the wiper assembly and tray to allow me to see what I was trying to do. I was unable to press down on the release button and also wiggle off the male wire connector which is connected to the 02 sensor. Finally, after over an hour of struggling, I unbolted the small bracket that holds that 02 sensor connector to the block. It's a simple 10mm bolt and it was easy to loosen from it's attachment point on the block. Now I was able to turn the connector so I could easily see the release button. It was still difficult to release the wire connector but it eventually pulled out. I could not get a hand on both sides of the connector but I was able to press down on the button with a screwdriver. Wow, simple things are often the hardest part of the job. And since I had the wiper assembly removed, I changed the spark plugs before putting it all back together. The last time I did the plugs was 100,000 miles ago, and they really needed replacing after looking at them. BTW, I don't think removing the small coolant reservoir would work. The rear bolt on the reservoir is very very difficult to remove without removing the nearby large wire bundle, and I think it would still be difficult to get enough room to unscrew the bolt.

[@carlloeber]

It's amazing that you figured it out to do it from the top.. on the clip and the bottom to remove and replace it.. I would try it that way but now I've already riveted my shield back on .. the shield under the whole catalytic converter.

[@ChristopherJeremiahCullen]

Glad you were able to get it done, however you ended up doing it! I didn’t try it, but I did wonder about just unbolting that coolant reservoir to access the wire harness/clip for the sensor.. it is located pretty much directly beneath it.

[@HeiderSati]

Brilliant video, thank you very much for your time making it, I was looking for where exactly the darn thing was, thank you!

[@sanelatutaris15]

Thank you soooooo much! This was so helpful.

[@daleferguson1233]

😅your the only one got it from the bottom.. I'll try it your way😅

[@danielmalloy6093]

You were able to remove the old sensor with the heat shield still attached? That in itself is amazing. Chris can you take a quick look and see if this will work, its what I already have. 7/8-Inch 22mm Offset Oxygen O2 Sensor Socket Wrench Removal Tool Drive 3/8"

[@ChristopherJeremiahCullen]

For the sake of clarity. it seems worth saying that there are multiple heat shields which people seem to have trouble with: (1) the large one that covers the exhaust manifold. And (2), the small heat shield around the o2 sensor itself. Neither got in my way.. it seems like the other people who had to destroy the heat shield around the old o2 sensor were just using a socket that didn’t have thin enough walls to seat fully around the o2 sensor (hence the beauty of having the right socket. Schley Products 66750B is what worked for me. If I were you, I’d just test it on the new o2 sensor you’re wanting to install to make sure it seats fully and you won’t have trouble there. The socket you have sounds similar, but only way to know is give if a shot ). I also saw people removing the large heat shield around the exhaust manifold… it seems that would only be necessary if you were trying to do it from the top - didn’t have any issues with it from the bottom, though it is tight and a bit tricky to get the wrench situated up there, as shown in the video (around 6:00)

[@danielmalloy6093]

Thank you@@ChristopherJeremiahCullen

[@carlloeber]

No I opened up the shield and replaced the downstream and then riveted up the shield again.. I've ordered the upstream sensor but haven't got it yet.. I was too cheap to buy the denso..

[@carlloeber]

What kind of troubleshooting did you do to decide that the upstream O2 sensor was bad? Did you also replace the downstream? Was the engine missing really badly? Was there any kind of troubleshooting other than that that you did?

[@ChristopherJeremiahCullen]

I was getting an error code that pointed to the o2 sensors (I think it was P0138). I had placed the downstream o2 sensor already, as it’s very easy to access, and that didn’t solve my problem, so I figured it must be the upstream sensor

[@carlloeber]

@@ChristopherJeremiahCullen That's where I am right now.. I replaced the downstream first.. I ordered the upstream but haven't started to put it in yet..

[@jamiemcdonald4279]

​@@ChristopherJeremiahCullenP0420 is the code ime getting which I'm told is either the catalytic converter or o2 sensor. I just replaced the downstream sensor but the light just came back on so now I'm gonna try this before the cat.

[@xj1223]

My only diagnosis was looking at the entire situation: Before replacement of upstream sensor: -gas mpg went down to 30-33 mpg over an extended period of time, and that happened at the same time period when I got a p0420 error code. After week of thinking about replacing the sensor, the code magically went away with no intervention on my part, so I continued to drive it for another thousand miles but gas mpg still was bad. -I know the downstream sensor was replaced 10k miles earlier but not the upstream sensor. -My Gen 2 Prius had 190k miles My conclusion: given the high number of miles on the car and the bad mpg, plus my web research about causes of the P0420, I went ahead and replaced the upstream sensor (see my prior comments on this process). There may be other reasons that a P0420 error message was triggered, but I figured I could eliminate one potential reason by replacing it. My results: recently went on a 1,000 mile road trip and I got 45-48 mpg. No more error code.

[@JamesJon1187]

@@ChristopherJeremiahCullen I got that same error code and came to the same conclusion after research. Thanks for confirming this is probably the fix! And thanks for posting this solution!!