Engine Troubleshoot

Why Is The Check Engine Light Flashing? (Causes, Symptoms and Solutions)

check engine light flashing

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What causes the check engine light to flash?

A flashing check engine light can indicate a problem with an engine sensor, a vacuum leak, a problem with fuel delivery, fuel ignition or a major mechanical problem resulting in engine misfire.

If you don't have access to an OBD diagnostic tool, it's sometimes not that easy to figure out what exactly a flashing check engine light is trying to tell you.

However, you shouldn't ignore it as a the check engine light is usually triggered to warn you about something wrong with the engine in your vehicle.


What is the Check Engine Light (And What Does it Do)?

The engine Electronic Control Unit (ECU) is constantly receiving information from its sensors and using this information to control the various engine systems to keep the engine running smoothly.

When you start up the engine, you'll usually see a few different lights flash on and then off in the instrument cluster on the dashboard. This is the ECU doing a check of the various engine and car systems such as fuel delivery, engine temperature, airbags, the ABS system among others. 

Car dashboard icons

Common dashboard warning lights that come on and off during start up

If everything is ok, all of the lights will go out.

One light that you won't always see is the check engine light. On some cars this will flash on for a second when the engine starts and then will go out again. On many newer cars, you'll never see this light unless there is a problem.

So the first time most people will see the check engine light flashing at them is when there is something wrong

Essentially, if a check engine light blinking is telling you that the ECU has detected something wrong with the engine.

Depending on the make and model of your car, the engine light may flash continuously, illuminate constantly and be orange or red in colour. 

It's important to check right away what the engine light is trying to tell you, and the best place to start is by checking the user handbook that came with your car.

Why Is My Check Engine Light Flashing?

What does a flashing check engine light mean? The check engine light flashes because the ECU has detected a misfire condition on your engine and a problem with one or more engine components.

Usually, the ECU will only light up the check engine light when there is something wrong with an engine electrical circuit or a failed engine sensor. It may not always flash if there is an out of range signal from an engine sensor.

But if there is a severe engine problem detected, it may cause a flashing engine light to get your attention. It's very important that you take action right away.

Some older vehicles have an SES (service engine soon) light. A blinking SES light is usually the ECU telling you to service the engine now. It's not the same as the check engine light, so the vehicle should be ok to drive.

Service Engine oil pressure

The service engine light

The ECU is constantly checking your engine performance by receiving real time information from its sensors. As soon as a problem is discovered the ECU reacts, by comparing sensor information that it is expecting with actual live information.

Depending on the problem, the check engine light might flash or can turn a constant red or yellow.

Check Engine Light Meaning

The check engine light usually flashes if it detects an engine misfire. There are usually two engine systems that could be responsible for an engine misfire and a subsequent flashing check engine light.

The ignition system and the fuel delivery system.

A faulty ignition system will not be able to ignite the fuel properly and thus cause a misfire. On the other hand, a poor fuel delivery will cause a lean mixture condition that also will trigger engine misfires.

Ignition Coil

Faulty ignition coils can cause the check engine light to flash

The following is a guideline of common causes for engine misfires.

Engine Misfires can be caused by a problem with the Ignition System, these problems can be caused by:

  1. Bad or defective spark plugs
  2. Oil on one or more spark plugs
  3. Bad or deficient spark plug wires
  4. Bad or deficient ignition coil(s)
  5. A bad or defective crank position sensor (CKP)
  6. A bad or defective cam position sensor (CMP)

Engine Misfires can also be caused by a problem with the Fuel Delivery System, these problems can be caused by:

  1. Bad, deficient or clogged fuel pump
  2. Bad or clogged in-line fuel filter
  3. Bad or clogged fuel tank filter
  4. A bad or deficient fuel pressure regulator
  5. Bad or deficient fuel injector(s)
  6. A bad, deficient or clogged mass air flow sensor
  7. A severe intake manifold leak
Diagnostic OBD reader

In most cases, using a professional automotive scanner is the best way to diagnose and determine what component is at fault.

Common Check Engine Misfire Symptoms

Along with a blinking check engine light, you may experience one of the following symptoms:

  1. Rough idle
  2. Difficulty in starting your engine
  3. Poor fuel performance
  4. Lack of power
  5. Distinctive misfire sound on your engine
  6. Gas smell on your tailpipe
  7. Rotten eggs smell coming from your tailpipe
  8. Black smoke coming from your tailpipe

Check Engine Light Codes - what are the most common?

The check engine light comes on when the ECU logs a problem with the engine. Every error stored in the ECU has a particular "P" code associated with it. 

When the check engine light lights up, the best way to figure out what's going on is to hook up a diagnostic reader to read the stored codes. Once you have the code(s) then it's a lot easier to identify the faulty component.

Here are a few of the most common P codes associated with the check engine light.

  1. P0300 - Random Misfire Detected Code
  2. P0440 - Evaporative Emission Control System Malfunction
  3. P0401 - Exhaust Gas Recirculation (EGR) Flow Insufficient Detected
  4. P0420 - Catalyst system efficiency below threshold (Bank 1)
  5. P0299 - Turbocharger/Supercharger A Underboost Condition

How much does it cost to repair a flashing check engine light?

The cost of repairing a flashing check engine light can vary greatly, depending on the cause of the problem and it is impossible to predict the cost for every type of problem.

In many cases, it is a cheap fix and can be resolved by changing some service items such as spark plugs or engine filters. This can cost between $50 and $100, and maybe a bit more if you hire a mechanic to do the work.

If the problem is caused by a faulty engine sensor or ignition coil it can get more expensive. Engine sensors such as a mass air flow sensor or camshaft position sensor can cost anywhere from $40 up to a few hundred dollars to repair. Ignition coils are usually more expensive, with cost of repairs running into hundreds of dollars, or even in excess of $1000 on newer premium vehicles.

Problems with turbochargers, EGR valves, fuel injectors and fuel pumps can cost anywhere from $150 to $800 to fix, depending on the severity of the problem (if a component needs to be replaced) and the amount of labor involved.

 

Why Is It Bad To Drive When The Check Engine Light Starts Flashing?

You should not drive your car if you suspect it is misfiring, as doing so can cause severe damage. 

blown cylinder head gasket

A misfiring engine can cause overheating problems and possibly a blown head gasket

Here are a few of the possible consequences of driving with the check engine light flashing:

  1. Catalytic converter damage. As a direct consequence of engine misfire, you may face a melting catalytic converter. Not only is the catalytic converter expensive, but could also cause other costly issues like engine overheating. 
  2. Engine overheating. With or without the CAT issue you could face an overheating problem. This, in turn, can potentially destroy your engine, starting with your head gasket.
  3. Cylinder head gasket failure. A burnt head gasket is something you should avoid at all costs. It can mix your engine oil with coolant and cause damage to the engine block. That would mean a major engine repair, way more expensive than a catalytic converter.
  4. Piston head failure. Continued misfires can sometimes lead to damaged piston heads, another costly repair.
  5. Burnt exhaust valve(s). Another very common mechanical issue triggered by an engine misfire is one or more burnt exhaust valves. 

What should you do if the Check Engine light starts blinking?

blinking check engine light

Modern engines are complicated and it can be difficult to figure out what is wrong when you see the check engine light

If the check engine light comes on at start up then don't drive the car. If it comes on when you are driving then pull over as soon as it is safe to do so.

Driving your car with a flashing or solid (not flashing) check engine light can cause serious damage to the engine, as outlined above.

Once you are parked safely, you should perform a quick inspection of your engine as follows.

  1. If possible, take note of the engine coolant temperature value in the instrument panel. Shut off the engine immediately if you suspect the temperature is above normal values.
  2. If the temperature is normal then open the hood and look for abnormal noises in the engine. If you hear any unusual sound then shut off the engine.
  3. Assuming everything is normal (temperature and sounds) go around to the back of your car to check for signs of problems from the exhaust. Any gas smell, rotten eggs smell or blue, white or black smoke is a bad sign. Shut off the engine if necessary.
  4. If you don't know how to fix the problem yourself then call your mechanic or tow service.

Common Questions Related To Check Engine Light Flashing

1. Check engine light flashes when accelerating

If the check engine light only flashes on and off when your car is accelerating. This can be a sign of a problem with the fuel delivery system such as a worn fuel injector or blocked fuel line or fuel filter. When you accelerate more fuel is needed to increase the rate of combustion. If the fuel is not available, then this can cause the engine to misfire, causing the check engine light to flash.

It can also be a sign of a bad of failing idle air control valve. If it is faulty, the amount of air entering the engine can be impacted causing the engine to misfire or even stall. A quick way to check the idle air control valve is to run an engine diagnostic and see if error code P0505 is present.

2. Check engine light is flashing and then stops

An intermittent flashing check engine light is very common. It can have a wide range of causes, and sometimes the cause can resolve itself. As outlined above, a flashing check engine light is caused by a problem with the ignition or fuel delivery system (or both). If the check engine light randomly comes on and then off again over a number of weeks it could point to a failing component such as a fuel injector, mass air flow sensor, ignition coil or camshaft position sensor. 

If you run a diagnostic check and there are no error codes present then you need to start checking things like hoses, electrical connector leads to sensors, the fuel and air filter, spark plugs and so on for problems.

If there are error codes present, try clearing the error codes and check engine light and see if it comes back on again. Engine trouble codes may point to an intermittent problem with a sensor and this can be a sign that a component is failing and should be replaced.

3. Check engine light flashing and car is shaking

If the check engine light is flashing and your car is shaking (when idling or accelerating) this can be caused by a failing idle air control valve or by an engine misfire. Engine misfires can be caused by a wide range of problems such as bad spark plugs, faulty coil packs (or ignition coil), engine sensor issues to name but a few. 

If your car starts shaking, you should cut the engine right away so as not to cause any damage. Run a diagnostic check to see which error codes are present before carrying out a physical check off the engine.

4. Check engine light flashing then solid

Sometimes the check engine light will flash for a few seconds and then stay on. This is usually a sign of an intermittent problem with a failing component that temporarily rectifies itself. For example, if you've got one or more failing spark plugs, ignition coils this could trigger the check engine light and a temporary random misfire in the engine.

Even if the engine continues to run normally, the check engine light will stay on until the error code is cleared from ECU memory. If after clearing the error code, the check engine light comes on again, then you should investigate further so as not to cause engine damage.

5. Check engine light flashing before starting the engine

A flashing check engine light when the engine is off is caused by an incomplete emissions monitoring test. This is perfectly normal in many vehicles, and should rectify itself the next time you drive the car and the tests are completed.

This system is fitted to many Chrysler vehicles. If you turn the key to the on position but don't start the engine, a flashing check engine light means that the emissions testing is not complete. If the check engine light is solid, then you are good to go. The check engine light should go off once you start the engine.