Your car’s Check Engine Light (CEL) is a helpful feature that alerts you of potential problems with your engine or sometimes, transmission. If you can find what’s causing your CEL early on, you can prevent further damage and keep your repair costs from rising.
Learning how to read a Check Engine Light allows you to easily identify common issues and avoid paying for diagnostic tests at the mechanic (for example, simple issues like a loose gas cap that just needs tightening). You’ll also be able to confirm whether a more expensive repair, like a catalytic converter replacement, is actually necessary before you sign off on getting it done.
The simplest way to check a CEL code is by using an On-board Diagnostic-II scan tool (OBD2 scanner). This device plugs into a vehicle’s Data Link Connector (DLC or “OBD2 port”) and reads diagnostic data, which you can use to find out what your check engine light means. You can even spot intermittent issues or confirm repairs by using the scanner to look up stored code’s & time stamped entries. This can help you identify the most common causes for a check engine light easily, along with some live data.
Although this article provides step-by-step instructions in Method 1 on how to check an engine light with a scanner.
We also detail how to check an engine light without a scanner in Methods 2 and 3.
Let’s get started.
How to Read a Check Engine Light With a Scanner | Fastest & Easiest Method
Instead of figuring out where to get a CEL checked for free and taking an adrenaline and anxiety fueled trip to the local auto parts store hoping your engine doesn’t break, you can check the light yourself using an OBD2 scan tool and save yourself the hassle. You can use a scanner to diagnose issues with your vehicle’s engine or emissions system.
Cars manufactured after 1996 can be scanned with an OBD2 tool. Earlier models have an OBD1 port and typically require an OBD1 scanner to read diagnostic data.
In Method 1 we will cover how to read your code with an OBD2 scanner. Keep in mind that an OBD1 scanner should generally follow the same steps as OBD2, but OBD1 was not a standardized system like OBD2. Some of the details, such as port shape and the number of pins are different for each car maker (for cars made before 1996) and these variations could not be taken into account without over complicating the instructions below.
With that said…
Method 1: Read Your Check Engine Light With a Scanner (Bought or Borrowed)
Whether you bought or borrowed your OBD2 device, the process of how to check codes for a Check Engine Light is the same.
1. Safety first
With your vehicle parked in a well-lit and well-ventilated area, turn off the engine and set the parking brake.
You don’t necessarily need any protective gear if all you’re doing is scanning for Diagnostic Trouble Codes (DTCs). But, if you go poking around under the hood, wearing safety glasses and gloves is a good idea to avoid mishaps.
2. Locate the Data Link Connector (DLC) or OBD Port
Next, locate your vehicle’s trapezoidal, 16-pin DLC (OBD2 port). This is where you’ll connect your OBD2 scan tool to access the diagnostic data.
Most of the time, the DLC is located below the steering wheel and a little to the left or right. Don’t be afraid to use a flashlight if you’re having trouble finding it.
Rarely, the DLC may be in the center console, either in the storage bin behind a cover or by the shifter. This deviation is found in some Ford, Nissan, and Honda models.
Consult your car’s service manual to find the exact location of its DLC if you’re stumped.
We have more on finding your cars’ service manual in Method 2: step 2 of this article.
3. Turn on the Ignition, but Don’t Start the Engine
Now that you know where everything is located, you can turn on the ignition, but don’t start the engine. Just turn the key until it clicks into the accessory position i.e. – when the interior lights and radio (usually) come on but the engine isn’t running.
Most OBD2 scan tools read stored diagnostic data, not live information. If you start the engine during a reading, you may overwrite/clear any stored trouble codes and render the scan void.
For models with keyless ignition, you can activate accessory mode by pressing the ignition button once, sometimes twice. Just be sure to keep your foot off the brake pedal, otherwise the engine will start.
4. Wait 5 Seconds, Then Plug the OBD Scanner Into the OBD Port
Now it’s time to connect the OBD2 scanner to the OBD port. Ensure the device is turned off and plug it into the port, making sure it clicks into place.
The OBD2 connector is a trapezoid shape, so it only fits in 1-way. This means you don’t have to worry about plugging it in incorrectly, it’s either plugged in, or it’s not. Just make sure at least 5 seconds pass after you turn the ignition on and before you plug the scanner in so the diagnostics can boot up properly.
Some OBD2 readers are self-powered and may turn on without being connected. Others require electricity from the vehicle for the screen to power on.
Some scanners, like ours here at FIXD, feature a Bluetooth connector that streams diagnostic data straight to an OBD scanner app on your mobile phone. The app then guides you through the scanning process and gives you the information you need in simple terms that are easy to understand. This makes figuring out how to read a Check Engine Light easier and more intuitive than ever.
5. Let the Reader, Read
With everything securely connected and the ignition on, it’s time for the scanner to read your car’s diagnostic data.
Depending on the device, scanning may begin automatically, or you might have to select “Scan” from the on-screen menu.
Readings typically take 5 minutes or less, depending on the scanner model and scan type. Once complete, you should see a prompt on the screen.
6. Write Down Vehicle Information and Mileage
Before reviewing error codes in your OBD2 scanning tool, jot down a few specifics about your vehicle first, like its year, make, model, mileage, and engine type.
You’ll need this data later when diagnosing the cause of the CEL, determining the severity of the problem, and taking the necessary steps to resolve it. Keeping a record of this data is also helpful for future reference if the issue occurs again (The FIXD app automatically keeps a record of all your vehicle’s stored check engine codes, your scan history, as well as freeze frame data of when the code was thrown. It also tells you the severity of the engine code and next steps to take to fix it.)
7. Find OBD Codes in the Menu – Identify Problems
You can now move on to reviewing the DTCs. Different scanners have slightly different menu layouts, but you should be able to navigate from the home screen to the option for finding codes.
Trouble codes usually begin with a letter, followed by a 4-digit number, like P0301, P0016, P0420, etc., corresponding to a specific vehicle issue.
Some scanners may provide a brief description of the engine code, while others may require additional research to determine the cause.
Check out “The Most Common Diagnostic Trouble Codes | DTC Directory” to find your code and what it means.
The FIXD scanner & app automatically provides these explanations in plain English for the codes it pulls. Get FIXD, and you can stop digging through mechanics forums and endlessly scrolling through car repair videos on YouTube.
How To Read Your Check Engine Light Without A Scanner | 2 More Ways to Find Your Problems’ OBD Code
If you don’t have an OBD scan tool handy or don’t want to invest in one, don’t worry. There are still ways to find the meaning of a CEL that don’t involve using a scanning device.
In this next section, we’ll cover Methods 2 and 3, showing you how to check an engine light codes without a scanner.
Method 2: Use Your Odometer & Count the Number of Flashes
If you don’t have an OBD scanner, you should still be able to check your code via the odometer. You can reset and trigger the odometer to display your trouble code or in other models, initiate a CEL blinking sequence that represents a trouble code.
Step 1: Version 1 – Reset The Odometer
The first step starts with an odometer reset but, you’ll have read the light from the display or count the flashes afterwards.
- First, you can reset an odometer by turning the ignition to the “on” position without starting the engine, then pressing and holding the trip button until it reads “0.0” or “ODO.” In some models, you need to hold the trip button and a separate reset button to reset the odometer.
- After resetting the odometer, turn the ignition off and wait a few seconds before turning it back on. Once you turn the car back on, you should see a fault code (DTC) flashing on the odometer’s display or see a flashing check engine light.
- Lastly, you’ll have read the light from the display or count the flashes depending on your car
- If the fault code shows up on your odometer display, write it down.
- If instead you get a flashing Check Engine Light, you’ll have to count the number flashes to get the code. Skip to step 2 of this method and grab your cars’ service manual to determine what code your flashing light is indicating. If you don’t have a service manual for your car, we’ll tell you how to find it (usually for free) in step 2.
You’ll need your cars’ specific service manual because the number of flashes and what code it corresponds to is vehicle specific, so reading codes without a scanner for a Chevy, for example, differs from reading codes without a scanner for a GMC, Ford, Toyota, Honda or Subaru.
If Step 1: Version 1 didn’t make the code appear on your odometer display or cause your check engine light to flash, try Version 2 below:
Step 1: Version 2 – Reset The Odometer & Flip The Key In The Ignition Back & Forth Multiple Times
- Start by turning the ignition to the “on” position, then resetting the odometer by holding the trip button until it reads “0.0” or “ODO”, just like Step 1: Version 1 above (check to see if you have a separate reset button if holding down the trip button alone doesn’t reset the odometer).
- Then, turn the ignition key to the “on” position without starting the engine and hold down the trip button. But this time, flip the key back and forth between the “on” and “off” positions (without starting the engine) at least 3 times, it may take up to 5 times for some cars.
- Finally, release the trip button while the key is in the “on” position, and check the display for a blinking trouble code. Again, if the fault code shows up on your odometer display, write it down.
If you get a flashing Check Engine Light only, you’ll have to count the number flashes to get the code. Again, go to step 2 of this method and grab your cars’ service manual to learn how. If you don’t have a service manual for your car, we’ll tell you how to find it (usually for free) in step 2 below.
Step 2: Watch the Flashing Light and Decipher the Code
If your car doesn’t show any trouble codes in the Odometers’ display and the CEL is blinking intermittently, you must count the blinks.
It’s important to count the blinks, and whether they are short or long, correctly, to ensure a proper diagnosis.
Because human error is more likely with this method, it’s less reliable than an OBD2 scan tool. Still, it should at least let you know if the issue is severe and requires immediate attention, as long as you count the check engine light flashes correctly.
In order to decipher the blinks you’ve counted, you’ll need your vehicles’ service manual, it will help you determine the code.
In most cases the counting method is the same for fault codes, it hasn’t really changed in years. There are long blinks and short blinks. Long blinks are equal to “10,” while short blinks equal “1”. For example, 6 long blinks and 1 short blink would be equal to 61. You would then search for the number 61 in the “Diagnostic Trouble Code (DTC) Chart” provided in your service manual to find your fault code.
But, what if you don’t have a service manual?
How to get a service manual for your car:
Search “{year} {make} {model} service manual PDF” with your cars’ year, make, and model in Google, once you have the PDF, look for the “Diagnostic Trouble Code (DTC) Chart” inside.
If you can’t find a free PDF, you may need to purchase the service manual for your car and search for the “Diagnostic Trouble Code (DTC) Chart” there.
Method 3: Use a Paperclip to Access Your Diagnostic Trouble Code (Counting Flashes)
There’s still hope for checking your engine light codes without a scanner.
Method 3 involves using a paperclip to access your DTCs. It’s not as straightforward as Method 1 or 2 but is still feasible if you can figure out which terminals in your OBD port to connect. Unfortunately this is not well documented for every car. This method is usually reserved for cars made before 1996 (OBD1) since the scanners for these vehicles are more scarce.
Quick Warning: Working with your cars’ OBD system in this fashion may risk causing a short in your car’s system and damaging it. While this doesn’t appear to be a common problem with the paperclip method for most people, our research for this article indicates that some DIYers have caused further damage to their car using this method. Proceed with caution. Also, although damages generally have financial repercussions, safety should be your number one priority. Be careful and make sure what your are doing is safe before you do it.
By searching “{Make} OBD paperclip” you can usually find a tutorial for using the paperclip method for your specific car and find what terminals in your OBD port to connect. Otherwise, you may need to look at your service manual if no other resources are already available online and figure out what ports to connect (not recommended for beginner DIYers).
Step 1. Find Your Vehicle’s Diagnostic Plug
Like the first 2 methods, you’ll start by finding your car’s OBD diagnostic plug, which is usually mounted below the steering column (a little to the left or right) but above the pedals on the vehicle’s driver’s side.
Step 2. Bridge the Wires
Locate the 2 terminal holes in the OBD port/DLC that you must connect for your car.
Using a plain paperclip, straighten one end and bend it into a U-shape. With the ignition off, insert the paperclip into both holes, creating a bridge between the terminals. Now turn the ignition to the on position (do not turn on the engine).
You should be able to see the CEL flashing if the bridge is successful. If it doesn’t flash, check your terminals to make sure you’ve connected the correct ones. If you’ve done this process correctly and the light doesn’t flash, it could indicate a problem with the ECU, in which case a professional mechanic may need to diagnose the issue. You could also get your hands on an OBD scanner if you wish to attempt diagnosing it yourself.
Step 3. Watch the Flashing Light and Decipher the Code
You should see the CEL flashing to indicate your trouble code if you’ve put your paperclip in the correct terminals.
Using the same methodology as earlier (Method 2, Step 2), where a long blink is 10, and short blinks are 1, you can decipher the trouble codes.
To find the number-of-flashes-to-fault-code conversion table for your vehicle’s make and model, you must review your model-specific service manual. See Method 2 for how to find your cars’ “Diagnostic Trouble Code (DTC) Chart”.
More On Reading Check Engine Lights:
How Do You Read A Check Engine Light For Old Cars Made Before 1996?
Cars built before 1996 didn’t have uniform OBD ports, so OBD2 scanners aren’t compatible. Instead, they have OBD1 ports (also known as Assembly Line Diagnostic Links or ALDL connectors) that are different for each car maker and can be read using the appropriate OBD1 scanner tool.
You can rent OBD1 scan tools from an auto parts store or purchase one online, just make sure it is the right one for your car.
What’s more, the process for how to check engine light codes with an OBD1 scanner is pretty much the same as the OBD2 device instructions outlined in Method 1 of this article.
If you can’t get your hands on an OBD1 scanner, you can try to manually read trouble codes using the odometer (Method 2) or using a paperclip (Method 3).
Most Likely Check Engine Light Causes, Repairs (+ Costs) & Codes
There are many reasons your car might display a Check Engine light. The most common causes include:
- Loose gas cap
- Bad spark plugs and wires (engine misfire)
- Low oil and oil pressure
- Malfunctioning O2 sensor
- Catalytic converter fault
- Mass airflow sensor failure
- Engine overheating
- Transmission problems
- Battery issues
- Vacuum leak
- Exhaust gas recirculation valve failure
- Check Engine Light is on for no reason or malfunctioning
- Failing aftermarket alarm
Whether you get your cars scanned or not, check out: “The 13 Most Common Causes For A Check Engine Light | How To Diagnose Them” if you want to learn how to diagnose a check engine light.
And if you want to double check your diagnosis and estimate the repair, check out the articles in the table below for the most common DTC codes for the most common makes and models. We also cover repairs, and repair costs (based on our scanner data):
Most Common Check Engine Light Codes & Repairs By Make & Model |
Related Car Lights That Can Help Diagnose The Issue
When trying to diagnose a CEL, other dashboard lights can provide insight.
For example, if you notice the battery light is also on, it could indicate a battery or alternator problem. Similarly, if the temperature gauge is reading high, it could suggest an engine overheating issue resulting from low coolant, a bad thermostat, or a bad water pump for example.
Another example is the ABS light. If illuminated along with the CEL, it could indicate a problem with the brake system or wheel speed sensors. Likewise, if the airbag light is on, it may point to a faulty airbag or sensor.
Note that while these other lights can give some indication of what’s going on, it’s always best to perform a proper diagnostic test to accurately diagnose the problem.
In our 13 Most Common Causes for a Check Engine Light article we cover other lights and symptoms for each CEL cause.
DIY vs. AutoZone vs. Mechanic: Checking Your Check Engine Light With an OBD Scanner
While you can try visiting an auto parts store like AutoZone, where they can run a diagnostic test on your car for free, the diagnosis may still be up to you. These stores typically use an OBD2 scanner and can provide you with a list of trouble codes. But you may need to diagnose the part that’s broken yourself. Auto parts stores may also refuse to reset the check engine light due to company policy even if the light was only caused by something as simple as a loose gas cap. If you do need to reset your light, you’ll typically need to do it yourself or get your car repaired and have the mechanic reset the light.
If you do take your vehicle to a mechanic or dealership to check your engine light, they’ll likely charge you about $100 – $200 for the diagnostic test. Still, they can provide a more comprehensive report than an auto parts store in most cases and give you a quote for possible repairs.
How long does a diagnostic test take on a car? About an hour, often putting the cost of the test at a shop at about $100 – $200. Some mechanics may waive the fee if you agree for them to repair the issue.
Finding a mechanic you trust is great. The next best thing is to use a product like FIXD that tells you the meaning of your check engine light and what the possible repairs are in plain english.
Ultimately, the decision to DIY or take it to a professional for testing depends on your wallet & your comfort level with diagnosing automotive issues.
If you want to save money on repairs and check engine light tests, take a look at the FIXD Sensor and app. We don’t just sell you a gadget to keep in your glove box, we offer an app full of information to help you fix your car as quickly, easily, and affordably as possible. FIXD tells you why your check engine light is on, how serious it is, and what steps to take next. If you’re not comfortable with DIYing repairs, the app can guide you to a certified and trustworthy repair shop in your local area.
With FIXD Premium, you also get access to our FIXD Mechanic Hotline to help you do at-home repairs. You can talk with a live mechanic over the phone who will walk you through diagnosing your check engine light step-by-step with our app, on your phone. Click here to try FIXD today for just $19.99 (normally $59).
How To Reset The Check Engine Light
It’s pretty easy to reset a Check Engine Light and it can be done with or without an OBD2 scanner. Here’s 4 ways to do it:
- Clearing your check engine light with a scanner is accomplished by pressing the “Clear” button on your scanner once you’ve read the code. Pretty straightforward. This is the simplest, quickest, and most guaranteed method.
To clear a light without a scanner, there are 3 other options,
Before resetting your CEL, please make sure you check the warnings in our article about these CEL resetting methods. Particularly, disconnecting and reconnecting the battery and driving to reset the light should be given a second thought before proceeding. Doing either of these incorrectly can damage your car. Depending on the issue with your car and its year, make, and model, you may need to use a different resetting method to avoid making your problem more expensive.
FAQs About Codes & Check Engine Lights
Can a Car Throw Codes Without a Check Engine Light?
Cars can throw codes without a Check Engine Light (CEL) being lit. There are two types of diagnostic trouble codes:
- Pending codes – generated when an issue is detected but it isn’t severe enough to trigger a CEL
- Stored codes – generated when an issue is detected, and triggers a CEL
*Note that while pending codes won’t turn on a CEL, they can still be retrieved using a diagnostic tool.
Are Check Engine Lights Time Stamped?
Check Engine Lights (CEL) are time-stamped. The code that triggers the CEL is logged in the vehicle’s on board computer along with the date and time it triggered the light. This information can be retrieved using an OBD2 scanner.
Time stamps can help determine whether an engine issue is intermittent or persistent; or even help confirm a vehicle’s maintenance and repair history.
If the Check Engine Light is Off Does that Mean Your Car is Fine?
While a lit CEL indicates an issue with your engine or emissions control system, the absence of the light does not necessarily mean everything is fine.
There may be underlying issues that haven’t yet been detected by the car’s onboard computer. Unless you’re scanning your vehicle daily, the best you can do is maintain your vehicle and investigate any symptoms that arise.
How Can I Prevent My Check Engine Light from Coming On?
Routine services like oil changes, fluid checks, and engine tune-ups can keep your car running smoothly and prevent potential problems that would cause a check engine light. Additionally, avoiding rough driving and using high-quality fuel can also help.
There is no surefire way to prevent a CEL from coming on. Still, good maintenance practices can help minimize the chances of it significantly.
Josh Barrett is a writer hailing from the great state of Alaska. While describing himself in the third person is not his forte, writing about any and all things automotive is. After 13+ years hustling in the exciting world of car sales, he took off to travel the world with his dog Teemo. Josh has written for several reputable automotive sites besides FIXD, including Vehicle History, AutoChimps, and more.
