Why is my “check engine” light flashing and my car shaking?

The ‘check engine’ light flashing and your car shaking is a sign of a severe problem that needs immediate attention.

As you may know, the check engine light (CEL) helps you know when there is a problem with your car’s ignition, fuel, emissions, and exhaust systems. The onboard computer triggers the CEL light to prompt you into fixing the issue.

This article will dive into the few reasons why the CEL is flashing and your car is shaking. We also talk about what you should do in case your vehicle is experiencing this issue.

Reasons why CEL is flashing and your car is shaking

Faulty spark plug

A majority of spark plugs are rated to work properly for up to 80,000 – 100,000 miles, after which you should have them replaced. The spark plugs will become dirty over time due to oil, carbon, fuel, and high temperatures from the engine. The dirt and eventual material deterioration will damage the electrodes on the spark plugs causing them to fail.

Failure to replace the spark plugs after the recommended number of miles will result in a few car issues that can prompt the vehicle to shake and trigger a flashing CEL. The symptoms of faulty spark plugs include reduced gas mileage, hard starts, lack of acceleration, and rough idling, which we will dive into below.

Reduced gas mileage

According to the National Institute for Automotive Service Excellence, worn-out spark plugs can reduce your vehicle’s fuel economy by up to 30%. That equates to approximately 94 cents per gallon at your local gas station.

The spark plugs are responsible for sparking the air and fuel mixture in the engine to create explosive combustion that drives your car. Any faults in these essential parts will cause less fuel to be ignited thereby wasting a substantial amount of fuel in the process. Eventually, the CEL will begin to flash, and the vehicle will start shaking.  

Lack of acceleration

If your vehicle is combusting less fuel than it usually does by each crankshaft rotation, then the acceleration will also reduce. Your car will start performing sluggishly once the spark plugs begin to fail. You can quickly pinpoint the problem with the spark plugs if the lack of acceleration is accompanied by reduced gas mileage.

Hard starts and rough idling

An empty gas tank, faulty or dead battery can cause your vehicle to experience hard starts. However, in the case of a flashing ‘check engine’ light and car shaking, faulty spark plugs are usually the cause. Old and malfunctioning spark plugs will have a hard time producing sparks leading to hard starts.

Furthermore, the faulty spark plugs will produce uneven sparks that will cause the engine to idle roughly. Various reasons can cause rough idling. However, in the case of a flashing’ check engine’ light and car shaking, rough idling is usually a symptom of faulty spark plugs causing the main issue.

Engine misfires

An engine misfire is caused when an incomplete or zero combustion appears in one or more cylinders. Your vehicle can continue to operate but the drivability will be inconsistent and unfavorable. Hence, you will know your engine is misfiring if you feel shaking or hesitation when driving the vehicle.

The engine can misfire if there is a problem with the air and fuel mixture or if the spark plugs are faulty. A malfunctioning cylinder can also be a cause. The most prevalent reason is usually a lean condition, implying either little fuel or too much air in the combustion mixture. Here are the symptoms of engine misfires:

Excessive exhaust smoke

The smoke can be caused by a rich air-fuel mixture or a carbon buildup. You may notice a white and sweet-smelling exhaust smoke or even a black one. Leaks can also lead to discolorization of the exhaust smoke. Excessive exhaust smoke can be a symptom of engine misfires causing the CEL to flash and the vehicle to shake.

READ MORE: White smoke from the exhaust when idling: What is the situation?

Unusual smell

Oil, coolants, and other fluids can leak out of a cylinder that is not functioning properly. The fluids themselves have unusual smells that the average driver can notice. Furthermore, the fluids might get burnt through the combustion in the cylinders causing the CEL to flash and your vehicle to shake due to unprecedented actions.

Abnormal sounds

Engine misfires are one of the deadliest faults a car could have since the problem can quickly worsen over time, damaging the entire engine system. An engine misfire will present itself as a popping sound or a backfire from the engine bay.

The backfiring happens when one cylinder gets burnt by the combustion in the next cylinder instead of the fue. The condition is prevalent in engines that have one or more cylinders that are faulty or not working. The abnormal sounds might be a sign of engine misfires.

Power loss

Your vehicle will start running on fewer cylinders the moment you have engine misfires in multiple cylinders. This will cause a loss of power since the power won’t be delivered in the same amount and precision as when the engine was functioning correctly. You will also experience minor power delays and hesitations when you apply the gas.

The misfires will be accompanied by other signs such as rough accelerations, stumbling from the engine area, and frequent vibrations. These signs, especially vibrations, will become more noticeable and frequent when you are idling and when your vehicle is operating at specific RPMs.

Frequent engine misfires at high RPM will often point to a lean condition. At high RPMs, the fuel injector and carburetor will struggle to provide enough fuel at the given speeds, causing an imbalanced mixture of air and fuel. Power losses can make the vehicle shake and will flash the check engine light.

Poor fuel pressure

Poor fuel pressure is associated with the fuel injector in your car’s fuel system. The fuel injector comprises a fuel rail on one side, and the other side has a compressor or turbo that boosts the air. The setup allows for fuel pressure regulation against air pressure keeping the fuel to air ratio at a constant 1:1.

This enables your vehicle to run smoothly and according to the manufacturer’s specifications. With that in mind, an imbalanced pressure may cause your engine to fail or take time to get cranked. The CEL will respond to this issue by indicating there is a problem.

Insufficient fuel pressure will come with a few symptoms: cold throttle, turbo lag, stalling engine, and low overall car performance. You may also experience engine misfires that will cause the CEL to flash and the vehicle to shake. Here are a few symptoms of poor fuel pressure.

Cold throttle

The primary sign that points to low/poor fuel pressure is an unresponsive throttle. Unstable fuel pressure will cause noticeable lags when you try to increase speed after engaging the accelerator. This is because there is improper or low fuel delivery to the cylinders causing them to malfunction and produce smaller combustion in the engine.

Stalling engine

If the fuel pressure is fluctuating and dropping suddenly, you may experience engine stalls when driving idling. For low fuel pressure, the engine will also have an improper mixture of air and fuel, leading to engine misfires and weak combustion. Stalling engines can be signs of poor fuel pressure.

Turbo lag

Vehicles with turbos rely on air and its pressurization to provide a turbo boost for maximum performance. The turbo system will fail to provide the needed spool if you have poor fuel pressure. Therefore, turbo lag may often point to poor fuel pressure.

Low performance

Low fuel pressure may cause the engine to accumulate less fuel, resulting in difficulty starting the vehicle. This is because your car needs a lot of fuel to start, and low fuel pressure will take time to provide enough fuel to the system. Your car will then experience low performances which is a symptom of poor fuel pressure.

Broken engine mount

Engine mounts are also referred to as motor mounts. The engine mounts are used to attach the engine body onto the chassis of your car. The purpose of this is to ensure that the operational, vibrating engine is well strapped and mounted onto the vehicle’s body to provide a smooth and stable ride.

These engine mounts are made of metal and rubber. The rubber is soft enough to provide shock and vibration absorption which minimizes the transfer of the engine vibrations to the chassis. The metal is strong enough and firmly mounted to provide support and stability thereby ensuring the security of the driver and passengers.

Once the stability is compromised, you may have a flashing CEL, and the car will shake on occasion. Here are a few symptoms of a broken engine mount.

Excessive vibrations

As much as broken engine mounts can cause vibrations, the most common reason is wheel and tire issues. These issues include ‘wheel and tire’ imbalance, loose lug nuts, separated tire tread, and irregular wear of the tires. Wheel and tire issues will cause excessive vibrations that can break the engine mount.

A broken engine mount will also cause extra excessive vibrations due to its motions, prompting the CEL to flash and your vehicle to shake.

Impact noises

The impact noises from the engine area are one of the major signs of a broken engine mount. The impact noises are caused by the movement of the engine, which is banging on various parts of the engine mount, causing it to make clunking and rattling noises.

Engine movement

Engine movements will be felt when you are accelerating. The motion will usually be in the form of a powerful backward surge when you accelerate forwards. You will feel another strong forward surge when you quickly stop the vehicle.

If you turn on a sharp corner, the engine movement will feel like an unusual side-to-side motion. These movements may be followed by impact noises letting you know the engine mount is loose or broken.

The rubber on the engine mounts will get worn out faster than the engine mount itself can get damaged. The process usually starts with worn-out rubber and then the engine movements which will eventually break the engine mount. Replacing the rubber seals will be a good solution in this case.

Read more: Honda CR-V “Check fuel cap” light: What it tells us?

What should I do?

The above causes are quite difficult to diagnose, especially when you are a novice at fixing car troubles. Even if you have the tools to perform the diagnoses and fixes, the process can be tedious work. This is because some of the shakings can come from many of the above reasons in unison with other unrelated issues.

A professional mechanic or technician is the one who will be able to accurately diagnose the problem and fix it quickly before it becomes fatal. Before taking your car to the mechanic, it would be better if you check for any stored codes on the onboard diagnostics system to have a clear idea of what might be the issue.

Another step you can take to take care of the ‘check engine’ light is to reset the light and see if it pops back up. A flashing ‘check engine’ light is more likely to pop up since it points to a severe fault. However, resetting the light can help eliminate any doubts about the problem.

You can reset the CEL by several methods, which include using an OBD2 scan tool, temporarily disconnecting the car battery, and pulling out the ECU fuse. You can also reset the light by turning the car on and off to see if the light comes back. Driving the vehicle for a while will also reset the light if the car has no underlying issues.

Once you have found out the CEL is legit and there to stay, use an OBD2 scanner to record all the stored codes in the onboard diagnostics system.

Conclusion

The CEL will flash only if there is a serious problem that needs your immediate attention. When the flashes are accompanied by your vehicle shaking, you know you need a mechanic as soon as possible. However, you can easily fix most issues that cause the CEL to stay lit. Unlike a flashing CEL, an always-lit CEL will usually point to minor issues such as a loose gas cap and faulty oxygen sensors. We recommend you see your local mechanic if you are not experienced in diagnosing the cause of the CEL.

Read more:

How can I disable Check Engine Light permanently?

Honda “maintenance required” light: What does it say?