Your Car's worth

There are four major factors taken into account when evaluating the worth of a car: mileage, market data, the condition of the vehicle and how well it has been maintained.
The value of a car is not always what Kelly Blue Book lists, but what it would cost to replace it.
Buying a New or Used Car

Ignoring that Check Engine Light   

When the first GM cars with onboard computers and diagnostic capabilities came out in the early 80’s, they could recognize a limited amount of problems and could store less than 20 trouble codes. It’s not unusual for an average car today to recognize and set 125 codes or more just for the engine and transmission.

Then there is Anti-lock Brakes, Traction Control, Air Bag, suspension and other systems that have their own codes. 

Some of these engine and transmission codes are for problems that usually won’t cause problems we notice while driving. We often hear, "that light has been on for years, I don’t worry about it anymore" or "Since this is a minor problem, can I continue driving it and not fix it right now?"
Unfortunately you only have one check engine light. If you ignore the light because of a problem that doesn't seem to affect the way the car drives, something else might crop up that will cause big problems and you may not know until it's too late because the light is already on.

Some problems that the light can come on to warn you about can cause poor mileage or be a warning that you may be left by the side of the road soon. Other warnings can be about things that can cause catalytic converter, transmission or engine failure.