I have a 2007 VW Jetta, my check engine light goes on and off but my car is running normal. The dealer wants to charge me$400 to diagnose it. I do not have this kind of money, I am a student. 
Are there any trustworthy FW mechanics that will diagnose my car free?
Try out the mechanic finder:
Also, go to a parts store (like an Autozone), ask them to read the codes in your VW (they’ll do it for free), write them down, and post them back here, we might be able to help.
Ok, I will try AutoZone and be back. Thank you
The diagnostic code is P2231. The AutoZone print out says I have something wrong with my heated oxygen sensor (HO2S11). Is this something that need immediate attention?
Please supply all pertinent info:
Are you 1st, 2nd, etc, owner
Present Mileage
Auto/Manual Tranny
Service History
Etc,
Etc.
I’m the 2nd owner. I purchased the car 2 years ago, it had 25,000 miles on it. The present mileage is 57,000 miles. It’s an automatic, 2.5 engine. Other than routine oil changes, tire rotations, and my 45,000? mile check up, I have not had any extra services done to it.