Replacing rear O2 Sensor

[a216vcti]

I got a check engine light last night for my rear o2 sensor, the downdraft one. I have a new sensor on the way and have the old one off the pipe. I was wondering if anyone has had the problem of the studs coming out of the cat. Both studs that were supposed to be stuck in the cat have unscrewed themselves instead of the nut on top and I am wondering what to do about it. My best guess was to screw the studs back in. I saw pep boys has a few that look similar.

The car is a 99 4R SR5 4x4 Automatic. I think it might be a california car because I went to autozone and they said that the front and rear 02 sensors are the same part number. I'm thinking it might just be a glitch in their system. Is there an easy way to tell?

 

[01thunder]

put the new one on and threads the studs back in.

 

[TheDurk]

I got a check engine light last night for my rear o2 sensor, the downdraft one. I have a new sensor on the way and have the old one off the pipe. I was wondering if anyone has had the problem of the studs coming out of the cat. Both studs that were supposed to be stuck in the cat have unscrewed themselves instead of the nut on top and I am wondering what to do about it. My best guess was to screw the studs back in. I saw pep boys has a few that look similar.

The car is a 99 4R SR5 4x4 Automatic. I think it might be a california car because I went to autozone and they said that the front and rear 02 sensors are the same part number. I'm thinking it might just be a glitch in their system. Is there an easy way to tell?

First, the front and rear sensors on a Cali. are ALWAYS different. Cali's have two cats, 49-state cars only one. Don't buy from PepBoys unless they are Denso sensors. Here comes my sensor 101 post before we go through it all again:

1. There are only three types of actual sensors: O2 flange (front and back), O2 screw-in(rear only), and A/F flange (front only). All other differences are wire length only. A/F's and o2's have different plugs. Wire length and specific part number varies by year, auto/manual,4wd/2wd, V6 or 4cyl, Cali./Fed. See #5 below.

2. Failing front sensors can degrade MPG's without throwing a code; if MPG's are out of whack, clean MAF and TB, then change front sensor if over 75k, change plugs if over 30k, change air filter if it needs it (visual).

3. All '96-'98 4Runners had the one-cat system. Cali'. systems with A/F sensors in front and two cats existed only in '99 and '00 and were sold all over the country, especially in 2000. Where the truck was sold means nothing except all trucks sold in Cali. were Cali.s in '99 and '00. Then, all trucks sold from 2001 on had the "Cali." two-cat system that then became the Federal 50-state standard.

4. To tell if you have a Cali., count cats or look at emissions sticker. Look at top left under ENGINE FAMILY: if it says ...AF, TWC(2), HO2S....it's a Cali. If it says ...TWC, HO2S(2).... : it's a one-cat, '96-'00 Federal.

5. Use Denso or Toyota sensors (made by Denso) only. You will pay a lot more for the exact same thing from Toyota. Get your Denso part number here:Find My Part | DENSO Auto Parts Then buy on Amazon, Rockauto or wherever is cheaper.

6. In salty states, the nuts will rust away and have to be replaced. They are stainless steel M8-1.25 nuts, part #90179-08059 at the dealer. Two per sensor. Denso/Toyota sensors come with the gasket included.

As far as the stud issue, lots of ways to skin the cat. Reuse the studs if that works, as suggested above. Use a bolt if the threads are still good. Buy new studs and nuts if you prefer. Or drill it out and use a bolt and nut. Whatever gets the job done.

 

[a216vcti]

Shit, i just ordered the rear from the dealer. Looks like i just spent an extra $100. Oh well.

It has two cats so it's a cali car. It looks like the 02 sensor was rigged in there to start. There were two different sized nuts on the studs. Since the studs are already out, would i be able to just thread a bolt into where the studs were?

 

[a216vcti]

Anyone care to chime in?