As the subject, my 2003 M3 failed the smog test.

The result for 15/25 mph failed in the HC(PPM) category.
Max is 51 for 15 mph and 35 for 25 mph, mine was 85 and 88.
This is much more than the limit.

I just did inspection 2 about 5 months ago at 48K in Dinan service.
No modification on this car, it is mostly used for daily driving.
Mileage is 50K now.

I went to dealer and asked them if there are recommendations.
The guy said $175 for the inspection, if something is wrong, then more. He said common is sensor or CAT. Price is $500 for sensor and $2-3000 for the cat.

Should I just let the dealer work on it? Or should I just ask Dinan service to check, it may be cheaper?

On the net, some people recommended to drive it for 20 minutes before doing the test. Does this really work?

I lived in the Fremont CA, can anyone recommend a smog station? Not just test station?