Being from California, I dont have to go through the vehicle inspection that others do. Smog check, yes but inspection, no. And I am curious about what is going on with a friend and his vehicle. I hope I can explain this right.

Last week, he took it for an inspection. Either during the inspection or just before it, his "check engine" light came on. No apparent reason that he could find. They ran the code and it came up some sensor.

They replaced the sensor. They then told my friend that he had to run his truck 100 miles before being re-inspected, to see if the light would come back on after the computer re-set. At 130 miles the light came back on.

He goes back to them and they check the code. This time it is a transmission sensor - different code, different area of potential problem.

So now he goes to a tranmission place and get quotes for the sensor.. and for a new tranny. His truck performs perfectly well.

So my question is this... to pass inspection, does someone have to replace part by part, by part until he can get his vehicle in and it passes or when he runs out of money? Why do all my red flags just wave frantically when I hear about this?