Check Engine light story
When I got home I hooked up my Harbor Freight ODB II scan tool and found out that the problem was Secondary Air Injector flow rate. I looked it up online and found a site that walks you through diagnosing and fixing the problem. I also found that replacement air injectors cost about $700.
I then took the car to a repair shop I've been doing business with. They offered to diagnose the Check Engine light for $135. I told them I'd already done as much and told them what the problem was. The service writer immediately went to "replacing the fan unit", without even considering checking the hoses. I deferred that, as I was really there to get the brakes replaced.
Later, when I got home I disconnected the battery cables for a while, then reconnected them. The check engine light was cleared, and hasn't come back on since. If/when it does I'll check the hose fittings first, then check to see if the fan housing is nice and tight, and whether the air pressure coming from it seems adequate. Only then will I even consider buying a replacement fan.
I guess the message behind all this is buy the ODB II scan tool and learn to look into these things before trusting a shop to do what's best for you.



