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Discussion Starter #1
I know that this topic has been beat to death with these two pain in the A$$ codes, but I was hoping for a little more insight. My 2003 4 runner V8 keeps throwing the same two codes, P0420 & P0430. I can disconnect the battery and the CEL will stay off for a few days but always comes back on. After much reading on the Forums I took it to the Dealership to try and verify a few things. Service writer did verify that it was the bank 1 and bank 2 sensors. BUT what he couldn’t tell me exactly is whether it was actually the o2 sensors that were bad, or the Cat's. Lots of help there. So now I am hoping to get some light shed on this situation before throwing away a chunk of cash. O2 or Cat’s? I bought the vehicle used and have not even made a payment on it yet. Can anyone shed some light on this? BTW: the truck has 83,000 miles on it, and I did clean the MAF sensor. Thanks
 

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"Rosco" Thread Derailer
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Hopefully some good news for you and it can all "end" soon.

Since you bought it used chances are slim you don't have the maintenance records but ya never know. :rolleyes:

Start with the O2 sensors, a hell of a lot cheaper than CATS! And they probably have never been done. With 83K miles, it's due.
Now don't get them at CarQuest, AutoZone or the like. Spend a few extra $$$ and get them from the dealer. Trust me, less headaches!

After you R&R the O2 sensors, get a can of Chevron Techron Fuel Injector Cleaner and when the tank is almost empty, pout the cleaner in and top off with a good premuim gas; Amoco Gold, etc.
Now take your truck out on the highway and run it!
You should be fine......:tu:
Good luck!
 

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"Rosco" Thread Derailer
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The least expensive thing to do would be to test the sensor. There are several write ups on how to do it. It isn't very complicated. You could just replace the sensor. I don't know what value you put on your time, but the part is going to run you about $150 or so and takes all of 15 mins to replace. It would be hard to call it if it is your cat that is bad or the sensor even if you knew the history of the 4runner, but with it being brand new to you it is almost impossible. The mileage is about the point where the sensors go bad and there really isn't alot that would make the cats go bad unless it was running real rich to the point that you could smell gas in the exhaust pipe. Did you ever find out if it had the TSB for the sulfur odor? If it did, it is possible they messed up the sensor or did not connect it properly.

In any case, as Flash stated, start with the sensor and work from there. I would strongly suggest that you go with dealer parts because you could compound your problems with aftermarket products.
 

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Discussion Starter #5
Hey guys, THANKS for your input. I took the 4 runner to a really reliable mechanic (in my opinion at least) and he was able to actually check the voltages thoroughly on the O2 sensors using his diagnostic scanner. I was even able to graph them. Seems that the voltage on them was fluctuating quite a bit and the waveforms were all screwed up. Definitely going to replace those first. Thanks again for the input!!! O and by the way RobXS, no, the guy never got the TSB done. Thanks for asking ;-)
 

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"Rosco" Thread Derailer
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Seems that the voltage on them was fluctuating quite a bit
Actually the voltage (mv) is suppose to fluctuate on an O2 sensor, that means it's working depending on the values.
If a voltage is a constant low or high or none at all, that can suggest a faulty sensor.
I'd start with bank 1 and bank 2 sensor 1. Then read the values of bank 1 and bank 2 sensor 2.
 

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Discussion Starter #7
hmm,, thats the kind of insight we need more of,, thanks for the tip. I did run across a schematic with the correct voltages for the sensors, If I find it again I will post it up here,, Thanks again
 
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