Engine light on sometimes 2006 trailblazer - 2006 Chevrolet Trailblazer

Invest in an OBDII reader. They range in price from $20-$400 and can do anything from just read codes when the engine light goes on, to real time data. Intermitent engine lights are tough, so next time it goes on, you can hook up your reader and find out what it is right then and there. Even for future problems, you can keep your mechanic honest by knowing exactly what's wrong with the vehicle. Buying a code reader will pay for itself the first time you use it.