Friday, September 08, 2006

The “Check Engine Light” Just Came On!

Imagine for a minute that you and your family are on the expressway on a Sunday afternoon, driving to your favorite vacation spot. All of a sudden, your red check-engine light comes on! What are you supposed to do? You are hundreds of miles away from home and it is very unlikely that you will find dealers’ service departments for your make of car open on Sunday. Should you keep on driving? Your only alternative under these conditions is to try and find a motel for the night and find a dealer the next morning.

Unfortunately, the answer is that you should not continue to drive the vehicle any further than you absolutely have to. The problem that caused the check engine light could be any one of hundreds. Potentially, it could be a very serious problem that could be made more serious (and more expensive) by driving the car. It could also be something so inconsequential as you failed to twist the gas cap tightly enough the last time you filled the tank. I have never completely understood why car manufacturers don’t enhance the warning system to differentiate between small problems that can wait and those that could be catastrophic. What a shame it would be to ruin a family’s vacation because they failed to screw down their gas cap tightly or some other minor problem that could have waited weeks to address! My guess is that the reason manufacturers do not enhance their check engine light computer system is simply because of the increased cost. I’ll bet that the cost of a motel overnight would be a lot more than the manufacturer would have had to spend to make the stay unnecessary.

The vast majority of the time the check engine light comes on, it is not serious enough to rush to your dealer. The problem is that you can’t say for sure if this is one of those times. In fact, the service advisors in many dealerships are so used to check engine lights coming on for minor problems like loose gas caps that they often mistakenly advise customers not to worry about it and to bring the car in “when you get a chance”. This works 90%+ of the time, but that 10% when it is serious can be very expensive. In fact, if the car is under warranty and you continue to drive the car when the check engine light comes on, you could void your warranty. If your check engine light comes on, pull over to a safe place and check to be sure your gas cap is screwed on tightly. That is the problem more than half of the time. If that doesn’t make the light go out, bring the car to your dealer ASAP.

The dealer has a diagnostic machine, called a “scan tool” which deciphers the trouble codes stored in your car’s computer. This code doesn’t necessarily tell the technician exactly what the problem is. Usually it just indicates an “area of concern”. He must do further diagnostic tests to determine the exact problem. Often there are more than one problem and symptom. Sometimes a problem will cause the check engine light to go on and then the problem “goes away”. If the problem does not reoccur during a certain number of times that you start the engine, the trouble code is removed from memory. Most of the reasons your check engine light will come on are environmentally related. If our cars did not have to meet such tight emission standards, you would practically never have a check engine light go on. This is one of the prices we are paying for clean air.

All too often, the check engine light will come back on right after you have had your car worked on for that very reason. Many people immediately assume that the dealer did not fix the car right the first time and charged them for work that wasn’t necessary. This can be the case if the dealer’s technician was careless or wasn’t properly trained. But, not infrequently, the technician can do everything right and the light still comes back on after the repair is made. This is because there are often multiple problems that contribute to the symptom causing the check engine light to go on. Or, there could be a completely new problem unrelated to the first. Remember that there are hundreds of reasons that this one red light can come on. It takes a very well trained, conscientious technician to come up with the right fix.

The best thing you can do is to choose the dealer to whom you trust your car with great care. You do not have to have your car serviced at the dealer from whom you bought your car, but you should use a dealer franchised to service that make of car. Check with the Better Business Bureau, County Office of Consumer Affairs, and the State Attorney General’s office on the track record of the service department you choose. Ask friends and neighbors who drive your make of car where they have their car serviced how satisfied they are.


  1. Hi ,some great stuff here.Im an avid car lover and came across a site about Antique Cars# that I thought was worth sharing as they have some really fantastic resources,considering how old these things are now I really struggle to get good information so if you enjoy the vehicles of the past go like I do then take a look.

  2. Now I don't feel as cheated after reading this. The vehicle was just 2 yrs old at the time. Went to the dealer for scheduled maintenance, on my way home and nearly $800 less in my wallet the "check engine" light came on. Called the service dept. and was told to being the vehicle back the next day. Was shocked to get another invoice for $600+ of additional work. That's when I stopped going back to the dealer where the vehicle was purchases.


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