Ruedy4

iTrader: (1)

I have had my service engine soon light on for about ten days and i ran a cheap scanner on it to give me a rough idea of what it might be. the code# is P0420 and the scanner reads "catalyst efficiency below threshold" thats all it says, but it gives me the code twice everytime. i was running cheap gas for the first week or so that i got it (yes i bought it a few weeks ago) and after a little while i threw that code. so i switched to 93 octane and the light stayed off for about a week and now it comes back on all the time. Does anyone think what i'm thinking-that maybe its an O2 sensor or a cat problem?? Thanks for your help!

heavy6.0

iTrader: (69)

you could have a bad sensor now, did you scan it after switching back to the 93?

Ruedy4

iTrader: (1)

yep i scanned it before and after i put the better gas in and its the same code.

LS184

iTrader: (7)

could b a bad cat, or bad front o2's

Ruedy4

iTrader: (1)

i guess there is no way to tell without the proper scanner.....

WS6addiction

iTrader: (1)

P0420 is the drivers side cat, or rear O2 sensor.

If you do a search for "P0420", you'll find more info than you can read. This question gets asked about 20 times a month.

Ruedy4

iTrader: (1)

ok thanks i'll search it.

01WS6JACKLE

what year is your car? 01 and 02s had a problem with the cats going out and needing to be replaced. i got my car from the original owner and he gave me a letter that was sent from gm. the said it wasnt a recall but if the problem did occur. you have ten years from the original purchase date to get it fixed for free. or a 100k miles. i would just get some new cats if this is the problem.

9000th01ss

iTrader: (10)

My ex's car puts out that code. She can drive for weeks around town but once the car gets up to 60+ mph for x minutes the code comes on.

If you google the code it will give you several reasons that can make it set.
Some of the less obvious are coolant leaks into the combustion chamber, oil burning, vacuum leaks, and a few more. More common are cats and O2's.

Ruedy4

iTrader: (1)

well i followed all your advice and i took a risk and went to the dealer and they scanned it. it turns out it is the cat and its getting replaced for free!!

Ruedy4

iTrader: (1)

thanks for all your help guys!