How to Diagnose a Flashing Check Engine Light and Shaking Car

PDF download Download Article
Figure out what’s keeping your vehicle from running correctly
PDF download Download Article

You’re driving down the road when your car starts rattling. Then, the check engine starts flashing. Can you keep driving or do you need to pull over? What’s causing this to happen in the first place? All of this can feel kind of overwhelming, but don’t worry—you aren’t the first person to run into these issues and we’ll help you get to the bottom of this. Read on to learn why this is happening, what the ramifications are, and how you can fix the issue.

Things You Should Know

  • The flashing check engine light and shaking both point towards an engine misfire.
  • The problem is likely a bad spark plug or ignition coil, so replacing these engine components should fix the problem.
  • Do not continue to drive with a flashing check engine light and a shaking car. Pull over to the side of the road and call a tow truck.

Get Car Support Solve Any Problem

wH
Hi there! Do you have a question about how to diagnose or fix a problem with your car? I’ve read the manual so you don’t have to. Select your make, model, and year, then ask away!
*
*
Section 1 of 5:

What causes a flashing check engine light and shaking?

PDF download Download Article
  1. The flashing check engine light means that there’s a serious problem with your engine’s functioning, and almost always indicates your engine is misfiring for some reason. The shaking also points towards a misfire, since a vehicle will shake during a misfire. That rattling will increase the faster you’re going. [1]
    • To be specific, a misfire occurs when one or more of the cylinders in your engine isn’t moving, or when it moves at a rate it shouldn’t be firing.
    • Misfires will often mess with your acceleration. You may feel like your vehicle is losing power or you have to press the gas pedal harder to get up to speed.
    • A solid check engine light indicates that there’s an error detected in the engine or emissions system. This is also a big deal, but it’s less immediately serious than a flashing check engine light.
    2. Advertisement
Section 2 of 5:

Common Underlying Causes

PDF download Download Article
  1. This is the #1 culprit of these symptoms (especially on older vehicles). The spark plugs provide the spark needed to ignite fuel, and it’s one of the three ingredients needed in the fuel + air + spark formula that your engine needs to fire properly. Without spark in one or more of the cylinders, that fuel and air won’t ignite and your engine will misfire. This will cause shaking at idle that gets worse when you accelerate.
    • The Fix: Replace your spark plugs . Remove your fuel rail to access your spark plugs yourself, or take your vehicle to a mechanic.
    • Change all of your spark plugs at one time. If one of them has gone bad, the odds that others are about to fail are especially high.
      • You have one spark plug for each cylinder. So, if you have a V6 engine, you have 6 spark plugs.
    • You need to change your spark plugs every 100,000 miles (160,000 km) or so.
  2. If your spark plugs happen to be fine, the most likely problem is your ignition coils. The spark plugs send their spark through these coils to reach the cylinder, and the coil carries that current and distributes it smoothly. Without a functioning coil, the cylinder either won’t receive the spark, or the spark will be unevenly distributed and the cylinder will misfire. This will cause symptoms identical to bad spark plugs.
    • The Fix: Replace your ignition coils . This repair is a little more intricate than swapping out the spark plugs, so see a professional mechanic if you can.
  3. Is the shaking you experience when you accelerate more of a jerking forward or stuttering? Does your car feel too fast, then too slow? If so, the problem is likely your airflow sensor. A bad airflow sensor will cause an inconsistent amount of air to flow into the engine, which can lead to misfires. [2]
    • The Fix: Your sensor is most likely dirty, so read your manual to locate it, and unscrew it from your engine. Clean the sensor with any MAF cleaner and reinstall it.
    • If cleaning the sensor doesn’t solve the problem, it needs to be replaced. Purchase a model designed for your vehicle and install it.
    • Some people will try to bypass a bad air flow sensor to keep it from triggering problems. Unfortunately, this will eventually lead to serious engine damage. Don’t do it.
    4. Advertisement
Section 3 of 5:

Less Common Causes

PDF download Download Article
  1. Any interruption to the airflow that your engine uses in the fuel + air + spark formula will also cause your engine to misfire. The most common culprits here are a vacuum leak, which will cause tons of extra air to enter the engine, or a jumped timing chain, which will keep air from entering at all. As a note, air mixture issues will always have additional symptoms, such as loud noises in your engine bay or a loss of the power steering system. [3]
    • The Fix: Diagnosing the cause of an air mixture problem is a little more involved than most backyard mechanics can handle. See a professional mechanic to get an air mixture issue fixed.
  2. Your crankshaft sensors monitor your engine’s cylinders to ensure they’re rotating at the proper time. As a result, your vehicle probably won’t shake if the sensor is the only problem and the cylinders are actually firing at the right time. But if the sensor in your vehicle is somehow responsible for the cylinder firing, it could potentially cause your vehicle to shake. [4]
    • The Fix: The crankshaft sensor is usually kind of hard to access and calibrate, so see a mechanic to get this one repaired.
  3. This is more likely to cause a solid check engine light than a flashing one, but it could flash depending on the underlying problem. Your emissions system is responsible for sending noxious fumes from the engine to the catalytic converter, but if there’s a leak or problem with the system, those emissions may flow back into the engine and trigger the occasional misfire. [5]
    • The Fix: You may need something as serious as a new catalytic converter, or something as minor as a patch on a pipe. Since this repair requires dealing with toxic emissions, have a mechanic do this one.
    4. Advertisement
Section 4 of 5:

Can I drive with a flashing check engine light and shaking?

PDF download Download Article
  1. A misfiring engine is not a minor automotive issue. Your engine cannot safely continue to run if it’s misfiring, and continuing to drive may destroy your engine permanently. You could also lose power at any moment if you keep driving, which can lead to risky situations on the road. [6]
    • If this happens again when you’re driving, put your hazards on and gently coast to the curb. Once you can safely stop, turn the vehicle off and call a tow truck.
Section 5 of 5:

How to Diagnose the Exact Problem

PDF download Download Article
  1. Turn the vehicle off and locate the OBD-2 port under your steering wheel (it’ll be behind a panel in most cases). Plug an OBD-2 scanner into the port and turn it on. Then, turn your vehicle to the “on” position. Press “run” or “scan” on the OBD-2 scanner and wait for it to return a diagnostic code . [7]
    • That code will refer to a specific error. Look up the error in your OBD-2 scanner’s manual to determine what the specific problem is.
    2. Advertisement

Expert Q&A

Ask a Question
200 characters left
Include your email address to get a message when this question is answered.
Submit
      Advertisement

      Tips

      • It’s possible that your car shakes and your check engine light flashes on after you complete an oil change as the system re-pressurizes. These symptoms should go away after a minute or so. If they don’t, you may have a leak in your oil lines.
        Thanks
        Helpful 3 Not Helpful 3
      Submit a Tip
      All tip submissions are carefully reviewed before being published
      Name
      Please provide your name and last initial
      Submit
      Thanks for submitting a tip for review!
      Advertisement

      You Might Also Like

      Find Your Paint Code On Your Car Fast
      How to
      Determine Gear Ratio
      How to
      Clean an Abs Sensor
      How to
      Test a Temperature Sensor with a Multimeter
      How to
      Start Riding an ATV
      How to
      Test a Vehicle Speed Sensor with a Multimeter
      How to
      Tell if a Tire Is a Snow Tire
      3 Effective Methods for Repairing a Cracked Car Dashboard
      How to
      Roll Down the Windows With Your Key Fob
      How to
      Diagnose and Fix Low Engine Oil Pressure
      Running Out of Gas: What Happens to Your Car & How You Can Get Help
      How to
      Fix Sun Faded Car Paint
      How to
      Fill Gas in Canada
      How to
      Remove a Dent From a Quarter Panel
      Advertisement

      Expert Interview

      Thanks for reading our article! If you’d like to learn more about car issues, check out our in-depth interview with Hovig Manouchekian .

      References

      1. ↑ https://www.telegram.com/story/business/automotive/2015/09/20/flashing-check-engine-light-means/33518515007/
      2. ↑ https://www.carsdirect.com/car-repair/how-to-tell-if-you-have-a-faulty-mass-airflow-sensor
      3. ↑ https://www.repairsmith.com/blog/vacuum-leak-symptoms/
      4. ↑ https://www.telegram.com/story/business/automotive/2015/09/20/flashing-check-engine-light-means/33518515007/
      5. ↑ https://www.kbb.com/car-advice/why-is-my-check-engine-light-on/
      6. ↑ https://www.repairsmith.com/blog/is-your-engine-misfiring-here-are-6-possible-causes/
      7. ↑ https://www.underhoodservice.com/tech-feature-detecting-misfires-in-obd-ii-engines/

      About This Article

      Thanks to all authors for creating a page that has been read 69,522 times.

      Reader Success Stories

      • Deanna H.

        Oct 5, 2023

        "Flashing check engine light article was very helpful. Thank you."
      Share your story
      If you buy through links on our site, we may earn a commission .

      Did this article help you?

      Advertisement