nightfox915

So my 2005 scion tc has been running really lean for the past year I've had that p0420 code on as well so first things first was to check the gas cap bought a new one code was not eliminated. Second I bought a lower oxygen sensor, code not eliminated. Third bought the Cat cleaner hoping it would erase that code, no dice either. So I took off the upper bank sensor and checked for continuity and results that there's an open circuit the car has 175k miles on and looks like the stock sensor lol. Just ordered a Denso 234-9041 Air Fuel Ratio O2 sensor for 115.00 on eBay Brand New with warranty and returns accepted. AutoZone wanted to sell me one for 280.00 Oreilly's had one for 175.00 same product same brand as the one I bought; laughed at their face and left. My car would burn gas real quick that is the fuel air ratio was below that 45mv while my car cycled never passed its mark to indicate it was a good 02 sensor it should read and fluctuate between > 0.2 to < 1.0 volt. Well wish me luck for this is my last resource before I spend 400$ on a new cat converter. Anyone had this problem or heard of this to be the case a bad o2 sensor running lean aka crap.

errgelistic

I have a similar problem. Got a P0420 bank 1 code. I got 150k on my 05 tc. I was planning to buy a upper o2/airfuel but not sure if I should replace this or the whole cat?

have the Denso 234-9041 Air Fuel Ratio O2 sensor eliminated the cel?

nightfox915

I replaced the upper sensor and it gave me 105 miles without the cel coming on i tried it again and again by resetting the code and gives me 100 miles until the cel comes on so i really need to change the cat

errgelistic

thanks! ill keep that in mind.. btw hows your oil consumption? mine just getting burned up every oil change i always had to 2 qt of oil.

nightfox915

Im using castrol fully synthetic 5w 30 its running nice and smooth with a k n filter or mobil one filter are good too do you have an oil leak or is it burning white smoke?

errgelistic

im using mobil1 full synthetic and mobil1 filter 10w 30. have a slight oil leak on my valve cover. no white smoke. i will need to replace the gasket soon and see if it works.

Marvelicious

I had the p0420 code, and some rough idling. It turned out that all the material from my manifold cat was coming apart and clogging the second cat. Bought a low mileage used manifold off ebay and problem solved. This might be a special case, since it's quite possible I (and/or the PO) damaged the front cat diagnosing the ignition coil troubles that the car had when I bought it. Still, it might be worth dropping your S pipe and taking a look at the condition of your cat material. If I remember correctly, I paid around $150 for a manifold with 20k on it. $250 more for brand new just didn't seem worth it to me.

Also of note, it won't help if the o2 sensor is actually burnt out, but sometimes you can get some more life out of a clogged sensor by taking it out and burning the carbon out. I've had good luck spraying the business end of the sensor with Non Cholrinated brake cleaner and then burning the gunk out with a propane torch. Not an exact science, but it has worked for me in the past.

nightfox915

I finally fixed the p0420 code resaulted i had a bad maf sensor and bad spark plugs so i bought those ngk laser iridium spark plugs and switched out the maf all codes are eliminated plus i took off the cat/manifold looked inside and was clogged so i punched out the inside honeycomb and put it back on. The car is running smooth with gained rpms and 100+ miles of better gas mileage

errgelistic

Bought a used CAT/manifold OEM off of a 07 tc at a local junk yard with the sensor for $250. Cleared the CEL. But 100-200 miles in, the CEL came back on -___-. I bought a new secondary o2 sensor (spipe) maybe that is the issue too?

Your CAT was clogged? what was the residue looked like? I have noticed small white particles was coming off my old CAT.

And how did you find out your MAF was the error when it is a P0420?

My car is really annoying lol