Eddie spent 35 years in the automotive business with Honda. He is an ASE Certified Master Technician and has bruised knuckles to prove it.
Your “check engine” light comes on when your car’s onboard computer (or PCM, Powertrain Control Module) records some kind of problem. This onboard computer runs your car so that it has optimum fuel economy and low emissions. The PCM creates a code indicating what part or system is malfunctioning (electrical system, oxygen sensors, and so on). Your tech can get the code from the vehicle and look up its meaning.
In the meantime, you’re probably wondering: what are the possibilities? Is there something going on in your car or in your life that triggered this “check engine” situation? Where should a mechanic start looking to find the problem?
The First Two Questions to Ask Yourself if the Check Engine Light Is On
- Is the car running normally?
- Is the "check engine" light flashing?
10 Diagnostic Questions to Ask If Your "Check Engine” Light Comes On
After you've determined if your car is running normally and whether the light is on or flashing, ask the remaining questions.
- Has your car been in the shop for service recently?
- Have you fueled your car recently?
- Did you possibly overfill your fuel tank?
- Have you installed any new electronic devices recently?
- Did your “check engine” light come on after driving through a deep puddle?
- Do you have excessive humidity in your car caused by a water leak?
- Do you live in a rural area where there are lots of critters?
- Are other warning lights illuminated on the dash?
- Did your car sit for a long period of time without anyone driving it?
- Were you the last one to drive your car?
What Does the Check Engine Light Look Like?
Don’t confuse your "check engine" light with your maintenance reminder (a light that goes on automatically to remind you it’s time for a routine service). If you’re not sure, check the index in your owner’s manual, under “warning lights.”
How Long Can You Drive With Your Check Engine Light On?
- Is the car running normally? If your car is running normally, and you have no problem driving it, the problem is not so severe that you need to panic. Of course, you should not ignore the light; it is warning you of some problem with the emissions system. When the light is on, your car runs on default parameters, not optimized to reduce emissions and increase mileage, and so you won’t get the gas mileage the car is designed to get. Just call your mechanic or dealer to make an appointment within a reasonable amount of time.
- Is the "check engine" light flashing? If it's flashing, it means you have a serious problem and you really should not be driving your car. It's flashing because it's saying “STOP!!! Hey, Look At Me!!!” It’s saying your catalytic converter is being damaged. It’s probably a good idea to call a tow truck at this point; you don’t want to add to the cost of any repairs that will be needed.
What Does the Check Engine Light Mean?
The check engine light is a light that the engine computer uses to signify that there is something wrong. They are orange, amber, or yellow, and not to be ignored!
How to Reset the Check Engine Light
The only way to "reset" the check engine light is by fixing the problem causing it. Thus, the 10 reasons I list below may help you reset your check engine light.
Why Is My Check Engine Light on? 10 Reasons Why Your Check Engine Light On
1. Has Your Car Been Serviced Recently?
If your car has been in the shop recently for service, it’s quite possible the technician has caused your "check engine" light problem. Sometimes a technician will forget to reinstall a connector to a sensor, or not snap the connector back together completely. Or he or she may knock a connector loose while doing a minor service.
On older Hondas, the oxygen sensor is directly below the oil filter, so a technician removing the oil filter for a routine oil change might spill oil onto the oxygen sensor. It’s just possible, though not common, that a technician wiping oil off the sensor damaged it somehow.
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2. Have You Fueled Your Car Recently?
If you didn’t tighten the fuel cap enough (or forgot to put it on altogether!), it can cause your "check engine" light to come on. All Honda fuel caps have a ratcheting device built into the cap to achieve a good seal and keep you from over-tightening the cap. When tightening your fuel cap, be sure to turn it enough to hear at least three clicks; that ensures the proper torque was applied. If your check engine light is on, simply check your fuel cap to make sure it is turned three clicks.
3. Did You Overfill Your Fuel Tank?
If you’re one of those people who like to top off the fuel tank, you need to break that habit, especially if you own a newer Honda. When the gas pump shuts off automatically, the tank is as full as it needs to be. To keep gasoline fumes out of the atmosphere, modern United States cars are required to trap the fumes and recycle them into the engine to be burned. Overfilling the tank can spill fuel into tiny vacuum lines and filters, which in turn can clog emission devices (like the "evap canister" being replaced in the three do-it-yourself videos at the end of this article). Soaking these devices in gasoline will cause the "check engine" light to come on. Replacing the damaged parts could be costly, but the time spent diagnosing the problem could be even more so.
4. Have You Installed Any New Electronic Devices Lately, or Had Them Installed by a Professional?
Everyone likes all the new gadgets available for cars these days, like backup cameras, thunder-booming stereos, remote car starters, high-intensity-discharge headlights, and rear entertainment systems, to name a few. It’s just possible that the person installing your device may have blown a fuse, or worse, may have tapped into the wrong wire and caused that dang "check engine" light to come on again.
Check to see that all electronics in the vehicle are working properly (e.g. dash light, 12-volt power supply, interior lights). If everything is working properly, I would either test all the fuses (using a test light or a voltage meter is the fastest way to do that) or return the vehicle to the person who did the work.
5. Did Your "Check Engine" Light Come on After Driving Through a Deep Puddle?
This isn’t common but it does happen. After driving for a while on the highway, your exhaust can get extremely hot; if you then happen to drive through a deep puddle, it is possible for water to cool the oxygen sensor too quickly and crack the material inside the sensor. The oxygen sensor is located under the vehicle, usually in or near the catalytic converter where the temperature can exceed 600 degrees. If this sounds like your scenario, take your car to the dealer or your local mechanic.
6. Do You Have Excessive Humidity in Your Car Caused by a Water Leak?
Water on the front or back carpet in your car will often be coming from the front of the car somewhere; water flows towards the back because of acceleration, and because the floor is tapered towards the rear of the vehicle. If the water is only visible on the rear carpet, the leak may be in the rear of the vehicle.
The most common cause of a water leak is the windshield; sometimes a newly replaced windshield will leak.
If a leaky windshield drips water on an ECU (Engine Control Unit) fuse box or any other control unit, this will cause an ECU failure and your “check engine” light will come on. Water is very damaging to all electronic devices (just drop your smartphone in water and see what happens).