Catalytic Converter

[jduawa]

Hello. Back in 2010 my 99 4runner 2wd (non cali) truck was failing emissions. We had the MAF cleaned and the front o2 sensor replaced and had an aftermarket catlytic converter welded on (oem was too much). Well, yesterday the truck threw a p0420 code. Item 1 in the printout from autozone is leak in exhaust before rear HO2S.

I looked under the truck and did not see any leaks. Now as far as I can remember and unless it is part of some kind of service interval I do not think the rear o2 sensor has been replaced, the truck has 220k miles on it. I have read many posts like this and they vary in solution from replace the cat to replace rear o2 sensor to replace front o2 sensor. Since the cat and o2 sensor bfore the cat was replaced 30 months ago I find it hard to believe it would be either of those 2 items.

So i guess it makes sense to try replacing the rear(after cat) o2 sensor. I have also read aabout differing part numbers on the rear o2 sensor. Is this the correct denso part ** Denso 234-4162 Oxygen Sensor and are there any tricks to getting the bolts off?

Does it make sense to try replacing this o2 sensor and see if the light comes back on? I cleared the light by disconnecting the battery.

Thanks

 

[TheDurk]

1. Yes, that is the correct number for your truck according to http://www.densoaftermarket.com/catalog/catalog.php?part=o2sn

2. At 220K, I would definitely try the rear O2 sensor. Changing mine cured a P0420 about 2.5 years and 40k ago and that was at 110k. I have a Cali. though, and those are more persnickety. You will hear some people say that the rear o2 sensor is a waste of time for a P0420; funny thing is they all seem to work at dealers.

3. The bad news is the after-market cats often don't last very long--so that might in fact be your problem. What brand did you get?

4. Your light will probably come back on as soon as the drive cycle completes again. This usually takes about a tank of gas. You should reset after changing the sensor so that it starts over. When my sensor went, I actually went a few months before it threw the code again. I went a year and a half just resetting until it finally was throwing a code every tank of gas.

5. On the nuts, it depends on how bad they are. Start with PB Blaster the night before. Use a 6-pt. deep socket. If it just rounds off try mashing on a smaller one. Those nuts are soft and the studs are very hard. I ended up just crushing some with a small pair of vise-grips and taking them off in pieces. The studs cleaned up nice. Some salt-zone dwellers have ended up replacing the stud with a bolt. Good luck. It can be a pain, but it gets done.

 

[jduawa]

thanks for the response, unfortunately I have no idea what brand of cat they replaced the OE one with. I looked on the invoice from the mechanic and it was subbed out to an exhaust/muffler shop. Maybe it wasn't that good of a cat since the subbed out charge was $300.

Thanks