Some places advertise free check engine light diagnostics. Be aware that this usually means they are using a code reader and are using just the trouble codes to determine what the problem is with your vehicle. If your vehicle has a oxygen sensor code, that does not mean the oxygen sensor is bad. That just means something on that circuit is bad. It could be the sensor, the wiring from the computer to the sensor, the computer, or anything in between. We use dedicated scan tools that are vehicle specific. Unlike code readers our scan tool gives us data the computer is seeing. We can operate different computer controls or force the computer to run tests right from our scan tool. When you come to us for a warning light or driveability problem we actually test the troubled circuit and confirm what the problem is before hanging parts. On intermittent problems we can take a movie of what the computer is seeing while driving your car. We then can view this information on a computer back at the shop.
What You Need to Know About Free Check Engine Light Diagnostics......