The check engine light really applies to OBD codes..... Things that affect emissions. You know, engine related things.

There's lots of other error codes that may or may not activate a different light. Such as the ABS light will come on or flash for abs related errors. The transmission overdrive light ...may flash.... For transmission related errors. There's a lot of errors that are stored in the PCM when things break that simply don't show up unless you scan the PCM.

The check engine light is not "the " light for everything thats wrong with your truck.