Your car's check engine light is your car's way of telling you it is sick and needs to see a professional mechanic. As many people do, you can stop by a local auto parts store, and they can plug in their scan tool and retrieve the trouble codes.
However, the difference between the scan tool that part stores use and the OBD-ll scanners that professional, licensed repair shops use is enormous.
The scanners that professional shops like Gearheads Garage in Bloomington, IL, use can cost way over $10,000 and perform many testing and diagnostic troubleshooting.
So, let's dive in and bring you up to speed on that warning light.
So, what is a check engine light?
The check engine light — a malfunction indicator lamp — is in constant communication with your car's computer. When something is wrong with your vehicle, the computer records a trouble code and sends a signal to the light to notify you that there is a problem and needs to be fixed.
It could be something as cheap and straightforward to fix, like a bad gas cap (seriously, we see this all the time) or something more severe like an internal engine component that is starting to fail. Either way, you should not ignore your vehicle's check engine light.
A brief history of the check engine light.
In 1996, auto manufacturers started to standardize a protocol called OBD-II, which formalized a list of diagnostic trouble codes and started installing a universal connector to access the car's onboard computer information.
The connector is usually located under the steering column and is relatively easy to access. Before 1996, automakers had their own unique engine diagnostic systems, mainly to ensure their cars were compliant with government pollution control requirements.
Depending on your car's manufacture, your check engine light is either orange, yellow, or amber, and again this depends on the manufacturer. If the light is solid and says "check engine," you should check it as soon as possible. However, if the light begins flashing, it indicates a more severe problem.
If it is flashing, you should shut off the vehicle and call a local professional shop. Driving the car could cause severe and costly damage.
The difference between service engine soon lights and check engine lights.
When it comes to your car, you should know there is a difference between the service engine light and the check engine light. The service engine light tells you that the vehicle is done for routine service or maintenance, like an oil change. Your check engine light means something is wrong and needs to be seen by a professional mechanic.
We provide free engine light diagnostic testing at Gearheads Garage in Bloomington, IL. But there is a way to check or retrieve the codes yourself.
You can buy an inexpensive code reader from an auto parts store or find one online. Prices typically range from $40-$500.
You can connect the code scanner to your car's onboard diagnostics (OBD) port, retrieve the codes, and search for the code's meaning online.
What does the check engine light scan code numbers mean?
Let's say you go to a local auto parts store or you have just purchased your very own OBD2 scanner. You plug it into the OBD port of your car, and it returns a bunch of codes. Now what?
You will need to do some research and find out what they mean. Here are some codes and their essential meaning. This list is by no means complete—just some examples. We recommend you speak to a qualified repair technician for a more detailed explanation.
P0171 or PO174 System Too Lean (Bank 1 or Bank 2) These codes can mean that you have more air entering your engine than fuel, and the computer is alerting that your fuel mixture is off. The codes, while similar, represent which side of the engine is causing the problem. However, there are several common causes of this OBD2 code, and it could be even just a false reading. Best to have it diagnosed by a licensed mechanic.
P0300 Random/Multiple Cylinder Misfire Detected
This code is typically returned when the engine experiences misfires in more than one cylinder and is not attributed to a single fouled out spark plug or a single clogged fuel injector. This could indicate low cylinder compression and multiple plugged fuel injectors.
P0340 Camshaft Position Sensor Circuit Malfunction
There are a good number of things that can cause this code. A lot of people go ahead and replace their Camshaft Position Sensor. Then they start driving their vehicle only to find that the check engine light comes right back on with the same code.
There are serval reasons this code can be tripped. If you want to save yourself a lot of time and pay for parts that might not fix your problem, we suggest you have a local shop run a scan and do a deeper dive into the diagnostic.
P0401 Exhaust Gas Recirculation Flow Insufficient Detected
This is a common code we see at our shop a lot. A lot of people will just see that code and think they need to replace the EGR valve, and the problem is solved.
This is one of the common ones where people just go replace their EGR valve only to find that it is not the problem.
Again, a standard code can have you buying and installing parts that do not solve your problem. Best to have an ASE-certified shop run a complete diagnostic scan.
P0420 Catalyst System Efficiency Below Threshold (Bank 1)
Your vehicle's PCM gets its primary information from the upstream and downstream O2 sensors. One of their essential functions is to make sure your catalytic converters correctly clean your vehicle's exhaust before it sends it out into the atmosphere.
When it senses that it's not, it will send this code. Before you run out and spend hundreds or even thousands of dollars on a new catalytic converter, check to see if there is not something else wrong.
Occasionally, a check engine light comes on when nothing is wrong with the car at all. It could be a temporary problem caused by a change in humidity or other crazy Illinois weather events. In such cases, the light will go off by itself after a short time.
These codes however are stored in your vehicles computer memory and can be recalled and cleared.
Again, the above is not an all-inclusive list of trouble codes, just examples of what some of the codes might mean.
How do I turn off a check engine light?
Most OBD2 code scanners you find at the parts store, or you purchase online will allow you to clear or reset the check engine light. However, doing this does not make your problem go away or fix your car. If you do not fix the underlying problem, the light will simply come back on later.
This is a trick that some shady used car dealers will use to sell a car. They will clear the codes right before the test drive. Or disable the check engine light. We have even seen cars come into our shop with black electrical tape covering the light area.
So, here is a car buying tip for you from your good friends at Gearheads Garage. if you are planning on test driving a used car, take it on a test drive to a local mechanic or parts store and ask them to run a diagnostic scan.
Some shops will charge a pre-purchase inspection fee. Here at Gearheads, we provide free scanning at our shop in Bloomington, IL.
Either way, it is money and time well spent that could save you a lot of headaches and money in the future.
No matter what, Don't Ignore That Light
Weather it is a service engine light, a check engine light, battery light or ABS light it's a good idea to have it checked out. Doing so now can save you a lot of time and money in the future.
If you have any questions or concerns about your vehicles' check engine light, just contact us here at the shop in Bloomington, IL or just bring your car in for a free diagnostic test.
If you would like to have your check engine light codes checked, just stop by our shop. No appointment necessary.
1805 Morrissey Drive, Bloomington, Illinois 61704, United States
07:30 am – 05:30 pm