I had a 2002 Nissan Sentra. The engine light went on when I went over 50k miles, which made it impossible to get a state inspection. So I brought it to Michael Jordan Nissan and paid over $350 for a rear O2 sensor. Later I found the part online for $118. The engine light remained on and I was told that I had to drive for 75-150 miles to 'recycle' the ECM.
When I returned, having driven nearly 500 miles with the engine light on the service staff expressed shock as they had recorded the light as off when the 'repair' was completed. I left it at the dealership all day again. Was told that the ECM (emissions monitor) was bad and needed replacement. The part would be ordered and I would have to return to leave it at the dealership for a third day.
Apparently the ECM was broken such that it always reported a bad rear O2 sensor. Coincidentally, of course, the rear O2 sensor was actually bad. Right. Of course, I have no way of knowing if the ECM unit was actually defective either.
Here's the really fun part - while waiting for the first attempt to diagnose an engine light a salesman approached me. I was thinking about a new car so I scheduled a test drive for a used 350Z. After enduring ham-fisted sales techniques with good cheer (e.g 'wow, you drive real good') it was time to find out the price. There was no sticker price and apparently you can't just ask.
We went into an office and the salesman made a 'phone call'. Then he through a fit over how low the price was for a couple of minutes before disclosing the price. The act was so over the top that it was hard to keep a straight face. Also, the price was several thousand over blue book. Everyone else in the region was selling the same car for several thousand under blue book. When I balked he left to bring in the 'sales manager'.
I had to wait over 15 minutes in the deserted dealership office. Then I had to refuse for 45 minutes as the sales manager forcefully demanded that I purchase the car then and there, while the original salesman stood blocking the door. They had the keys to my car, so I was stuck. I had to repeatedly ask for my keys in order to leave. For example, me: 'can I have my keys', salesman: 'sure I go get them' [doesn't move], sales manager: continues forceful demands that I sign documents.
I should have been more angry at the time, but it was comical. However, I am very upset about spending over $350 and two full days, on a $118 part which wasn't actually defective, before just giving up and selling the car, expired inspection and all, to Carmax.
I've learned that the foam casing of the ECM unit is acidic and damages the ECM board after 4 years or so, causing this problem. Nissan issued a recall on the foam, but this didn't prevent Michael Jordan Nissan from ripping me off (the ECM board was still under warranty).
I got tired of driving a car which couldn't pass a state inspection, so I now drive a BMW. Only a fool would do business with Michael Jordan Nissan more than once.