yet another p0420 question.

[wdhigh]

Few months back my cel came on and I went to autozone to get it read. Came back p0420 which the guy claims is o2 sensor. Says he's not sure which one and tells me front goes bad more often. Few weeks later I go in parts store and ask for an o2 sensor and guy looks it up and sells me a bosch for half of a denso. Get home and the plugs don't match. Carry it back and he double checks and still gets same part #. Then he pulls out a book and finds the correct one by using the book that shows different plugs. Now he finds one with the correct plug that is for 99-02 models and sends me on my way. I finally get around to changing the front yesterday and get the cel cleared and all is well. Starts easier and runs great. As luck would have it my cel just came back on, and shows p0420 again.

My questions are these,

1- do I just replace rear and go on my merry way?
2- Are bosch o2 sensors junk and I wasted more money
3- if I do go to replace rear is supposed to be different part #? Guy at parts store shows same part # for both positions. Not a cali vehicle to my knowledge.


Thanks in advance, have read and read all the related topics here and still had questions. Sorry to beat a dead horse guys, money is very tight and I am just trying to save what little bit I have.

 

[bhowle]

p0420 is a catalyst efficiency code, which doesn't necessarily relate to the front o2 sensor. Either your rear sensor has gone bad, or the converter(s) have gone out. How many miles are on your T4R? To properly diagnose this, you need to look at the o2 sensor readouts using a scan tool. Hold the engine around 2500rpm and you should see the front sensor switch between high (1.5v or so) and low (around 800mv) voltage, while the rear reads a steady voltage. If the rear switches similar to the front, your converter is bad.

 

[RAB]

I've had the same P0420 problem since when I purchased mine. I pretty much ignored it during the entire summer, however I'm beginning to sort it out. Here's what I've done.
1.) Change oil, (duh, but follow me here).
2.) BG 44K <-- didn't see that it did a whole heck of a lot.
3.) Cleaned the MAF sensor.
4.) Change the spark plug. Replaced with OEM spec NGKs.
5.) Change the PCV valve.
6.) Ran Lucas Oil fuel treatment.
7.) Cleaned the throttle body. Be careful here you might have an idle problem after you do it.
After all of this I've not have the P0420 in quite some time.
-Point being this that it could very well be the case that the engine isn't running as clean as it can be. My advised would be to exhaust all the cheap preventative maintenance problems then work your way to replacing the 02 sensor or a/f ratio sensor. <--- found of the CA model, that is a/f sensor then 02 sensor after the cat.
-I've got a 02 sensor (OEM) which I'll install once/if I get the P0420 again.
-And my truck is running a heck of smoother and cleaner.

 

[wdhigh]

thanks! Seems I have been given a little bit of wrong info in the past.

 

[RAB]

thanks! Seems I have been given a little bit of wrong info in the past.

I wouldn't say so. I was going down the same path as you were.

 

[TheDurk]

If you are buying Bosch sensors from someone who thinks one sensor works all 99-02 you are asking to become very familiar with that yellow light. Some '99 non-Cali. V6 DO use the same sensor front and rear. Some don't. They vary by transmission, engine, Cali./49-state, and year.

If all you were getting was a P0420, you want to change the rear, not the front. Good chance it cures your problem. It cured my P0420. If it doesn't, then you need a new cat (or the famous URD simulator.) The other possible cause is an exhaust leak, you should also rule that out. Still, a new rear sensor is a boatload cheaper than a new cat. If the sensor does not do it, get the test done as described by bhowie to confirm cat is not performing.

I recommend you get the correct Denso part number off this site (URD) and then get a new rear sensor wherever has the best price. Amazon has good prices, but LOUSY application info--you need to know the Denso number before you go there.

Look under the hood at the emissions plate (or count cats-Cali's have two) to find out if you are Cali. or not. If you changed the front, you would have been able to see both. I am pretty certain you are not, because an O2 sensor in front on a Cali. would probably give you a salad of codes in addition to p0420. I think the plugs are different, too.

Since it is 2-trip detection, CEL will stay off a while after it is cleared. Detection requires specific conditions, so two longer trips with varied conditions are required to resend the P0420.

Or, if money is way more important than time, take that front sensor you took out and put it back in the rear position (assuming URD shows front and back are the same on your rig). There is a reasonable chance you took out a good sensor and it may give you some miles in the rear.

Hope this helps....

 

[wdhigh]

Thank you.

I am really just guessing at this point what part #'s are correct. First one was what it calls for in 3 different parts store computers but plug would not match. Second one after looking at some other years, was kinda just stumbled upon. After looking it up it shows for 99-02.

Sorry to be a pain. Got a hook up on the bosch stuff and sadly is why I have not bought denso.

I am just really kinda shocked when parts don't match up but everyones computer shows the same numbers. Napa is showing the sensor I have as being good for front and rear so I will try that soon. If that does not work I will have to break down and get denso parts and start over. Although replacing the front has not cleared my cel, my mileage has been better past few days. I drive 65-90 miles a day so I notice it quickly.

 

[brian2sun]

I can't stand even going into vatozone anymore. I get more wrong parts than right ones from that place. Not that they're great, but I seem to have a lot better luck with Kragen/O'Reilly's.

 

[jsmarine]

I hate to tell you to get Denso since you have already bought Bosch, but I had a similar problem (P0420 code) and I bought Bosch sensors, and the correct ones according to the auto parts store. The CEL came back on after a few hundred miles with the same code. Before buying new cats (I have two, I'm a Cali 4runner) I did some research and found that when it comes to sensors, or anything computer related, it is best to go with OEM, (Denso). I guess Toyota's are just sensitive. So, I bought Denso front (A/F) and rear (O2) sensors and it did fix my problem, I cannot say for sure this will cure your problem since it could be cats, or something else, but just wanted to express my experience.

 

[RAB]

I can't stand even going into vatozone anymore. I get more wrong parts than right ones from that place. Not that they're great, but I seem to have a lot better luck with Kragen/O'Reilly's.

+1. I asked for plugs and got some shitty crap, then I handed the guy the NGK plug number from the shop manual. Can't really blame them, I guess...