Idiot Lights for Dummies

The pejorative term for them is “idiot lights.”  Every time you start your car they glow to greet you, but after a few seconds of engine operation they fade away, and, if you’re lucky, you won’t see them again until the next time you start the engine. These days, with cars more complicated than ever, it seems as if drivers are frequently confronted with these red and yellow indicators on the instrument panel but are not quite sure what to do about them. 

Experts say what you should do is pay attention to the warning being given.  It might seem as if your vehicle is “running fine,” but serious damage could result if you don’t pay heed to the warning light.

“Motorists need to be aware of the critical ‘big three’ warning lights,” said John Nielsen, Director of AAA Automotive. “They include those that monitor engine oil pressure, engine coolant temperature and the vehicle charging system.  To reduce the chances of vehicle damage and a roadside breakdown, these warning lights require prompt and proper action when they illuminate.”
It’s not too hard to figure out why these lights are designated the big three.  Each one is indicative of a symptom that could easily stop your vehicle in its tracks and strand you by the side of the road.  Two of them are also indicative of conditions that can cause catastrophic engine failure, which won’t only leave you stationary, it will also cost you thousands of dollars to repair.

The engine oil pressure warning light commonly displays an oil can symbol or the word "OIL." When the oil pressure warning light illuminates, it is signaling that the engine has lost the pressure that supplies lubricating oil to vital engine parts. Severe engine damage can occur within seconds. Of all the warning lights, the oil pressure light indicates the greatest potential for serious mechanical damage, and it also allows you the shortest time in which to take appropriate action.

If the oil pressure warning light comes on, and stays on, pull off the road immediately and shut off the engine. Unless you are in an extremely dangerous situation, do not attempt to drive the vehicle any farther. Operating the engine without oil pressure can significantly increase the extent of damage, turning what might just be a minor repair into a complete engine replacement.

The engine coolant temperature warning light commonly displays a thermometer symbol or the logo "TEMP." When the coolant temperature light illuminates, the engine temperature has exceeded the safe maximum. Until the rise in coolant temperature is reversed, the engine will suffer accelerated wear. If the increase in temperature continues, major engine damage will result.
The coolant temperature warning light is second only to the oil pressure warning light in indicating the potential for serious mechanical damage. However, the coolant temperature light does give you a little more time in which to take appropriate action. If the coolant temperature warning light comes on, quickly assess the situation. Steam or liquid coolant coming from under the hood are clear indications of overheating or a leak. But even if you don’t see steam or fluid, high coolant temperature can still cause major problems.  Pull off the road at the first safe opportunity and call for assistance. Continuing to operate an engine with an illuminated temperature warning light could result in a major damage and a significant repair bill.

The charging system warning light commonly displays a battery symbol or the logo "ALT" or "GEN." When the charging system warning light illuminates, the vehicle’s electrical system is no longer being supplied with power by the alternator. This means at some point your car will run out of stored electrical energy and stall.  But the good news is a charging system failure rarely results in serious mechanical damage, and of the "big three" warning lights, it is the one that gives you the greatest amount of time to take appropriate action. Depending on the electrical demands of your vehicle and the reserve capacity of its battery, you will generally have at least 20 minutes of daylight driving time before voltage drops to the point where the engine will quit.

If the charging system warning light comes on, turn off all unnecessary electrical accessories and drive to the nearest repair facility to have the vehicle checked. If you are some distance from a repair shop, drive to a safe location where you can call AAA or another towing or repair service.

In his line of work Driving Today Contributing Editor Tom Ripley hates being stuck by the side of the road. He reports on the car industry and the human condition from his home in Villeperce, France.