Top 10 Things To Do When Your Car’s Check Engine Light Goes On

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Published: 06th March 2012
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These tips will help you determine whether your vehicle needs a small, simple tune-up or large, serious repair.

For most car owners, the most confusing warning light on the dashboard reads "check engine.” This tiny suggestion might as well read “panic” for some people, as it can light-up for no apparent reason, resulting in an unplanned auto bill just to figure it out. I’m here to help you diagnose, and sometimes even fix, the various problems that can make you “see red.” So, the next time your “check engine light” comes on...DON’T PANIC! Don’t call your mechanic. Bookmark this website and let me tell you how to turn off that light.

There are a variety of problems that cause a car’s “check engine” light to come on, from a loose gas cap to a seriously misfiring engine, so it's vital to promptly diagnose the reason. "It doesn't mean you have to pull the car over to the side of the road and call a tow truck. It does mean you should get the car checked out as soon as possible," says Dave Cappert of the National Institute for Automotive Service Excellence (Virginia organization that tests and certifies auto technicians).

The first thing you must realize is that your car's “check engine” light is linked to its “on-board diagnostic (OBD) system.” This measures many of your car’s functions, such as engine speed, ignition timing, fuel mixture and gear shifts, to identify problems that could affect it’s performance and emissions. (Manufacturers originally used the OBD system to help technicians pinpoint problems, but these systems are now required by law.)

When the OBD computer finds a problem in the electronic-control system that it can't correct, it turns on a yellow warning light with a picture of an engine and the word "Check,” or it’s labeled “check engine," "service engine soon" or "check powertrain." Ignoring the warning could lead to damaging expensive components, or mean the car is getting poor fuel economy and emitting too many pollutants. "The 'check engine' light is reserved only for powertrain problems that could have an impact on the emissions systems," says John Van Gilder, General Motors' lead OBD development engineer. These tips will help you determine whether your vehicle needs a small, simple tune-up or large, serious repair.

Every new car comes with an “owner's manual” that explains what activates it’s “Check Engine” light. Cars feature different warnings to help drivers understand whether the problem is minor or major. If the "check engine" light illuminates, it will either blink or remain constant, depending on the problem. IE. In many cars, when a check engine light flashes like a yellow “stop light” (not just flickers on and off), or turns red, a severe problem, perhaps an engine misfire, needs immediate attention. Unburned fuel may be dumping into the car’s exhaust system, where it can quickly damage the catalytic converter, resulting in an expensive repair. When it remains lit, it indicates a minor problem, which can be attended to at your earliest convenience. (SO...flashing lights = BIG PROBLEMS ...just like when you see them behind you, as you’re speeding home to catch the start of the big game. *smile*) Now that you understand how your check engine light operates, here are a few things to try before paying a mechanic to diagnosis a car problem.

1. CHECK FOR SERIOUS PROBLEMS. If you’re driving, pull over to check for a serious problem needing immediate attention. First, look at the vehicle’s dashboard for signs of low oil pressure or overheating. Next, shut off the engine if either of these issues is present. Some cars feature 2 different "check engine" lights. The YELLOW one indicates a problem that can be fixed later on, but a RED light always means stop immediately.

2. REDUCE YOUR SPEED & ENGINE LOAD. When the "check engine" light is blinking, or you notice serious performance problems (IE. loss of power), reduce your driving speed. Also try to reduce the load on the engine. IE. If you’re towing a trailer, you should stop. Have the car promptly checked by a professional to prevent further damage.

3. CHECK YOUR GAS CAP. About 10% of the time the problem is simply, that the gas cap, which is about a $3 repair. In fact, this was THE most common issue over 12 years of data. So, try taking off your gas cap. Then, put it back on...and make sure it's on good and tight. Since the check engine light is connected to the car's emissions system, it comes on when there are fuel vapors leaking from the gas cap. In fact, a loose gas cap is the #1 reason the warning light is activated. NOTE: Sometimes it takes a few trials to reset the system. So, don't assume that was not the problem, just because the light does not go out after checking the gas cap. If the car is still running well, repeat this step a few more times. Letting the Check Engine light stay on due to a defective gas cap will release will decrease fuel economy by .5%, according to CarMD.

4. GET THE ENGINE’S DIAGNOSTIC-SYSTEM CODE. If it’s a GM vehicle with OnStar, call them for the code. The engine's diagnostic code is also available for free from an automotive pro. Many auto parts stores and franchise oil change and service shops will read the code for you for free (most often it’s a single letter, followed by numbers) ...but then pressure you to feel obligated to hire them for the repair. If you’re like me, and don’t like high-pressure sales, you can simply buy a diagnostic-system code reader for $50-$100, and get the code yourself. Some newer system scanners connect right to your smartphone (IE. GoPoint GL1).

Many cars also have a “secret” method to display the trouble code. Find instructions on how to do this via the Internet. Search for the car’s year, make and model, along with the words "check engine code" + "manually." With the trouble code in hand, research what it means at OBD-Codes.com (for on-board diagnostics codes) or ALLDATAdiy.com. Sometimes those websites provide instructions on how to repair the car yourself, BUT...
if it’s a major repair, the trouble code produced often refers to multiple problems. It may be best to work with a mechanic to diagnose the full extent of the car’s problem.

5. OXYGEN SENSORS Nearly 10% the "check engine" lights illuminated in 2010 were due a defective oxygen sensor. When this happens, the vehicle's engine-control computer defaults to a 'safe' mix of air and fuel. This makes the engine less powerful and pollute more...AND it also uses up to 40% more fuel. The gas alone would cost hundreds of dollars a year, for what would have been a $200 oxygen sensor repair, with parts and labor.

6. REPLACE THE CATALYTIC CONVERTER. Catalytic converter replacement is the third most common repair. But, if the vehicle has regular tune-ups, this should not be the problem, as today's catalytic converters are designed to last at least 150,000 miles. CarMD says that failure of “the cats” means repairs have been neglected for a long time. Replacement averages more than $1,000, but can cost up to $2,000.

7. REPLACE THE MASS AIR FLOW SENSOR. The #1 diagnostic trouble code (DTC) is "System Too Lean.” This is usually due to a faulty Mass Air Flow Sensor, which can affect fuel economy by 10-25%. Neglecting the car’s warning light, in this instance, can lead to expensive repairs. These will cost lots more than the $375 to replace the Sensor.

8. OTHER COMMON CAR FAILURES. According to CarMD, major engine work is the most expensive car repair, followed by replacing the “hybrid inverter assembly" ($7,000+). The third was Hybrid battery replacement, costing $2,300+. Other common car problems associated with the “check engine light” include: the exhaust gas recirculation (EGR) system, coolant thermostat and camshaft position sensor.

9. REGULAR TUNE-UPS ARE A GOOD INVESTMENT. In 13% of cases, according to CarMD, a misfire was the reason that motorists brought a vehicle in for repair with the "check engine" on. This was usually due to skipping scheduled maintenance and failure of spark plugs or ignition wires. That makes paying for tune-ups a sound investment. "The customer is really, in the long run, potentially hurting their pocket book by leaving that light on and ignoring it," says Jim Collins, a national training team leader for Ford Motor Company.

10. DON’T GO FOR A STATE EMISSIONS TEST. A lit "check engine" light, in a late-model car, will fail it in a state emissions test. NOTE: Don't try disconnecting the battery or erasing the trouble code to turn off the light. The vehicle's computer lets the inspection station know that its codes have been erased, which is an automatic fail. Then, you'll just have to go back for another inspection again.

BONUS TIP: Always address engine problems promptly, so you don’t become conditioned to ignore your car’s “Check Engine” light. If you can’t diagnose and fix the problem yourself, take it to a mechanic. Pay a little now. You’ll save a lot later. *smile*

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