I am in need of some advice. I had to have my O2 sensors replaced on my 08 MS3 for some unknown reason around 2 years ago at ~20k miles. I mentioned to them that I was getting poor gas mileage and that I thought that the engine was running rich - causing the O2 sensors to foul.
The dealership couldn't figure out why the O2 sensors went bad so early and were quite unhappy they had to replace them under warranty. They said they couldn't find any other problems or any evidence that the car was running rich, though it may have been they didn't want to replace anything else on their dime.
I bought the car used at 16k miles, I think it was repossessed. Either way, I don't know what the previous owner did to it, but if they did anything to it, it appears to have been returned to stock when I bought it.
I now have 37k miles and the CEL has come on again. I just went to autozone and they gave me the code P0421. They said it's either my O2 sensor or the cat going bad. He even said it was surprising since usually he doesn't see that code on cars with less than 100k miles.
I'm just wondering what you all thought. I don't want to replace the O2 sensors again if there is something else wrong with the car that is causing them to foul. I usually get about 18-9mpg around town, though I used to get about 14-15mpg before changing the spark plugs at 30k miles.
The dealership couldn't figure out why the O2 sensors went bad so early and were quite unhappy they had to replace them under warranty. They said they couldn't find any other problems or any evidence that the car was running rich, though it may have been they didn't want to replace anything else on their dime.
I bought the car used at 16k miles, I think it was repossessed. Either way, I don't know what the previous owner did to it, but if they did anything to it, it appears to have been returned to stock when I bought it.
I now have 37k miles and the CEL has come on again. I just went to autozone and they gave me the code P0421. They said it's either my O2 sensor or the cat going bad. He even said it was surprising since usually he doesn't see that code on cars with less than 100k miles.
I'm just wondering what you all thought. I don't want to replace the O2 sensors again if there is something else wrong with the car that is causing them to foul. I usually get about 18-9mpg around town, though I used to get about 14-15mpg before changing the spark plugs at 30k miles.
