A few years back I installed a head unit and I think it may have triggered a check engine light for my VSS, and turned off the spedo and odo. It was so long ago that I don't recall if it happened right after each other or not. A friend of mine told me it's possible that the head unit wiring could cause a problem because some cars radios increase the volume as you drive faster. Is this at all possible? The mechanic at pepboys couldn't figure out why the engine light was on, and I think this may be it.