SES light came on for a week and now off?????

[white01ws6]

The code was determined that the catalyst system efficiency for bank 1 is below threshold for the current engine operation conditions. (Bank 1 identifies the location of cylinder #1, while bank 2 identifies the cylinders on the opposite bank)

Everyone told me it was the cat and I was going to have my car go to the dealership for the federal emissions warrenty. But today AFTER I GOT GAS, the light went off. I dont know what the deal is. Maybe a bad tank of gas. Should I still take it in to the dealership. They said they will diagnosis it and if it is the cats then it will be free. But if it isnt the cat, I wonder how much it will be just for the diagnosis, probably a arm and a leg.

[2001NBMZ28]

Don't know why it went off, but I wouldn't bring it to the dealership for P0420 unless the light was on - around here they charge around $75 for "diagnostics." Give it a while and see if it comes back on, the cat warranty is good for 80K.

[chevyz28]

my car did the same thing. the light just turned off after about 2 weeks.

[02z28ls1]

If you've got a Autozone or Advance auto parts store they scan stuff for free around here-imagine that's nation-wide.There is a federal law warranty on emissions control stuff for 8 or 80,000-newer vehicles(not sure what year)have a 10 or 100,000.Find out what the code is for free first-if the problem was temporary the computer will drop the light after so many cycles on and off.