Over the years I have been using this local repair shop that specialized in Japanese cars, I have been going there now for over ten years and they are pretty competitively priced and always friendly, and I am not car literate some when they asked me to do something I usually told them to go ahead and do it and never questioned it or checked that it has been done.
Occasionally I will take my car to the dealers because some services the local shop don't do, tires, body work etc...
Recently I got a coupon from the Nissan dealer with a $9.99 oil lube filter service special so I took it in. They told me in addition to the oil change I need a fuel induction service on my 2002 Nissan Altima because there are tons of carbon buildup and that would be $160. I told them to not do it and that I would wait. I later took the Altima to the local repair shop when I had to replace the engine mounts and I told them to check the fuel intake and if I needed a fuel induction service, they told me yes I need it and it would be $80 so I did it. That was three weeks ago.
Today the engine light is on and the local repair shop is closed due to family emergency so I took it to the dealer again. They told me it's the catalytic converter that is failing and it would be $900 to replace it OUCH!!! but they also told me I really need a fuel induction service as the there are too much carbon build up.
So if there are too much carbon build up and I had that service done by the local shop three weeks ago, then something is wrong. I don't know how to check for it myself, so how can I tell what is really going on? I hate to think I have been going to a shop for 10 years and been paying for services that may or may not have been faithfully carried out.