Check engine light on

I have been told by dealers' service personnel that the check engine light seldom involves any critical part of the engine that is likely to keep the vehicle from operating. Most often it involves the emission control systems which are very complex and so very vulnerable to failing or generating a false alarm. So far with all of my cars and trucks the check engine light never involved a failing part that was critical except for the very last time with my diesel truck which has a special filter and two NOx sensors. In this case it was both a failed sensor and badly routed electrical wiring that was resting against the very hot EGR valve body and the AC compressor and so would have resulted in big problems and was definitely affecting DEF consumption and this can result in the truck going into limp mode with speed limited to 10 MPH which would mean having the truck towed to the nearest GM dealer.

There are OBD II devices that will read the error codes and sell for under $30. Problem I found with them is that as often as not the error code will not provide enough information as it is too general or it is erroneous as the computer is fooled by a faulty sensor or something as simple as not having the gas cap screwed on tightly. I carry a Bluetooth version as it is better than nothing and works with free software on my netbook. These also work with "smart" phones and Android if you have these. The best software is made for the Android platform. I use the Windows software and it is pretty crude.