ok so heres my problem had the check vcs and engine light come on, went to auto zone got the error code read. It came back with P0420, catalytic something on bank 1 friends told me it has to be a O2 sensor so take it to the mechanics they read the code say the same thing but then 4 days later the light comes back on same code, they replace the sensor again, everything is fine for like 2 weeks but now light is back on again, I have a 2006 GS300 with like 60k always use premium gas what can be causing this

 

maybe there is leak on exhaust pipe or catalytic converter gone bad.

 

With only 60k it would go bad?

 

I hope it is not catalytic on your case but catalytic converter can fault because of fouled plugs, bad O2 sensor, also u can damage it physically

 

First your mechanic need to check O2 sensors itself with voltmeter before he replace them. If O2 sensors are fine he need to check cat, by making two holes, one before cat and second one after cat, he need to check air pressure before and after, if there any difference probably cat is dirty.

 

also check for leak

 

I would second that, but be careful. Be aware that if you go that route, you might want to just go ahead and throw on an aftermarket exhaust. OEM cats=Not cheap.

 

Thanx guys ill be heading back to the shop today

 

Sorry, but your friends and mechanic are very very wrong...

P0420 is rarely ever an O2 sensor gone bad, but it can be... in this instance, it pays to watch sensor voltages to determine this for sure... which o2 sensor did you replace? your car has 4!

Couple more things - as Emilaman suggested, you can test for excessive restriction in a catalytic converter by checking pressures before and after the cat, however, that only tells us if a cat is restricted, not how well it is working... by all means, a cat may be restricted, but still not throw a code for an inefficiency...

Now, here is the kicker - your catalytic converter is under a federally mandated 8 year / 80k mile warranty... take it back to the dealer and demand it be replaced... From the EPA's website: "
What Are Specified Major Emission Control Components?

There are three specified major emission control components,
covered for the first 8 years or 80,000 miles of vehicle use on 1995
and newer vehicles:

* Catalytic converters.

* The electronic emissions control unit or computer (ECU).

* The onboard emissions diagnostic device or computer (OBD)."

http://www.epa.gov/OMS/consumer/warr95fs.txt

After (or before) the cat is replaced, you should try and find out why - with that few of miles, it shouldn't be having issues without cause, but you never really know. Things like misfires, bad O2 sensors, incorrect spark plugs, bad gas, and more can cause catalytic converters to go bad...

 

demand it to be replaced? I'm sure the dealer would want to inspect it before they just go installing a $1k plus part.

 

If I was sure it was bad, I would demand it be replaced... if they wanted to check it first, that is completely up to them...

your toaster breaks after 1 month of ownership, it has a 1 year warranty... it doesn't matter what how the company does it, but it gets fixed in the end, right? same thing - demand it be fixed...

reason I say demand is that I have seen many dealerships charge customers to replace cats while they were still under the federally mandated warranty...

 

thanx guys for all your advice, I took it to another mechanic a friend of a friend , he said that code means theres a problem with the cat, he sent me to strauss, to buy a cat cleaner comes in a green can, put that it run the car and hopefully it will clean it out. well 2 weeks later so far and light hasnt come back on. hopefully this cured the problem thanx again

 

Well a lil update the cures in the can didnt work, so took it to the dealer comes to find out it was an exhaust leak, dealer took care of it also did 3 recalls and no more problems