check engine light flashing

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

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A flashing check engine light is usually a sign that something isn't right with the engine in your car. 

The check engine light can indicate a problem with an engine sensor, a vacuum leak, a problem with fuel delivery (fuel filter or injector) or at worst a major mechanical problem.

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

It's never a good idea to ignore a flashing check engine light. The blinking light is on to warn you about something wrong with your engine.

So let's explain what the check engine light is for, what causes it to light up and what you should do when you see it flashing.

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. 

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, the check engine light, is there to tell you that the ECU has detected something wrong with the engine.

Depending on the make and model of your car, the 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.

What Is My Check Engine Light ​Blinking?

Usually, the ECU will only light up the check engine light when there is something wrong. 

But if there is a severe engine problem detected, it may cause the engine light to flash on and off 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.

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.

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.

If it receives a value that is out of range, then it will trigger the Check Engine Light on the dashboard. Depending on the problem, the check engine light can turn a constant red, yellow or will flash.

The Top Reasons Why The Check Engine Light Flashes

There are usually two engine systems that could be responsible for an engine misfire and a subsequent blinking 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.

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

If it's a problem with the Ignition System:

  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)

If it's a problem with the Fuel Delivery System:

  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 or several 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

The Top Check Engine Light Error Codes

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 Long Can You Drive With The Check Engine Light Flashing?

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

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 when the Check Engine Starts Flashing?

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.

Once you are parked perform a quick inspection of your engine status:

  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.