QUESTION: This radio commercial I keep hearing says you should take your car in right away for service if the check engine light comes on because you could cause serious damage to your engine. Also, they're saying the light is red. My light is orange, and it does come on sometimes, but usually goes back off within a day or two. Are there different kinds of check engine lights? I haven't taken this too seriously because the engine always runs perfectly and the car always passes the smog check. Should I?ANSWER: This year marks the 30th anniversary of the check engine light, and it seems there is more confusion than ever regarding its operation. Many years back, GM renamed the light "service engine soon," likely to reduce the number of tow truck bills submitted for warranty reimbursement. The standardized name now used by the repair industry is MIL, or malfunction indicator lamp. The light is yellow/orange, rather than red, as its urgency is not the same as an oil pressure, engine temperature, brake system or charging system problem.On vehicles built prior to 1996 the MIL will illuminate should the engine control computer detect an open or shorted electrical circuit in a sensor or actuator circuit. These vehicles have limited diagnostic capability with perhaps a dozen or two possible fault scenarios, and most detected faults are significant. Post 1996 vehicles are equipped with OBD-II (on-board diagnostics II), and go far beyond obvious circuit faults.Can you keep driving with a steadily illuminated MIL? If the engine runs smoothly and emits no foul odors, I'd look into the cause within a week. Should engine performance faults be evident or the MIL is flashing (severe engine misfiring is occurring), limp home as gently as possible and put the car in the shop the next day.The two worst-case scenarios are engine misfire and a grossly incorrect air/fuel ratio. A misfiring engine (thumps and shudders) emits huge emissions and will likely destroy the catalytic converter(s) if driven continuously under this condition. Unburned fuel in a misfiring cylinder also washes away lubrication, accelerating wear. An excessively rich air/fuel ratio can damage or destroy the catalytic converter and a lean mixture can cause harmful cylinder detonation. Symptoms of a rich mixture may be exhaust odors and/or smoke, a loping idle, and difficult hot-engine restarts.