Why Is My Check Engine Light On?

Oh no! Panic time.  My check engine light just came on, what do I do?  Visions of a broken down car, a tow-in, and a large repair bill at your local dealer all come crashing into your mind.  What's going to happen, now?

The First Thing To Do Is Relax

Realize that there are two engine lights on your instrument panel. One is actually called Engine and is usually red.  This light warns of problems in the engine itself related to oil pressure and coolant temperature. This light will tell you that you've not not added any oil ever or that you're overheated and should shut the vehicle down immediately, in a safe manner, to avoid damage.

The light is amber and is called "Check Engine".  A bit older vehicle may be labeled "Service Engine Soon".  Either way this light tells us that the vehicles onboard computer system has determined that there may be a problem in the vehicle's emissions system.  These types of failures will affect the quality of the exhaust coming out of the tail pipe of the car or possible the fuel mileage.  It rarely is a situation that will cause damage to the vehicle, hence the "Service Engine Soon".  In other words as soon as it is convenient, get on in there.

An exception to this would be if the Check Engine light were on and flashing.  This denotes that a engine misfire is occurring that is significant enough to cause possible damage to your catalytic converter.  A catalytic converter replacement could get expensive and it could keep the car from running until it is fixed.

Get It Scanned

The first thing to be done is to get the computer scanned for trouble codes.  After a detected fault the ECM (Engine Control Module) will store a trouble code related to the fault.  This is where the fun begins and sometimes the heartache.  Say you rush down to your local auto parts store and the counter person comes out to your car to offer a free scan.  He tells you the ECM has stored an oxygen sensor code and recommends you buy a sensor from him and your problems are over.  Unfortunately there may a dozen different oxygen sensor codes, many of which do not indicate that the sensor itself is bad.

Many thousands of dollars are wasted every year by people and shops throwing parts at a Check Engine Light without doing the diagnostic testing required to actually get to the real problem. A failure in one part can set a code in a related part.

What Do I Do?

Having your own Code Reader is benefit to a car owner. There are many on the market that are very inexpensive and will reads the codes and include a definition list.  The units will then clear the code and turn off the light.  If the light comes back on, then it may be time to make an appointment with the repair shop.

In the early 2000's most cars that were fairly new that pulled up to my shop with the check engine light on, had a code that indicated the fuel cap had been put on too loose.  All that was needed was to scan the ECM and clear the code and put the cap on better at each refueling.

So don't panic.  Know what your codes are, do a bit of research, and then if a repair is necessary you are in a better position to get it done right.  It's never the time to just buy an expensive part that you may not need and throw it at the problem.

Good luck.