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How to Fix Turn Signals Blinking Fast

These days, vehicles are safer than ever. This mostly due to added high-tech crash prevention features. But, let’s not forget about one of the most essential systems when it comes to safety: turn signals.

The smooth operation of these lights is crucial to ensure everyone arrives in one piece at their destination. But, what if your turn signals start blinking faster than usual? What does it mean and how can you fix it? Before you rush to the repair shop, take a minute to read this article. You will learn how to easily find the source of the problem by yourself and save some hard-earned money.

How does the turn signal system work?

On a basic system, as you would find on a motorcycle or most entry-level vehicles, the power comes from the battery. It goes through a set of fuses providing power to the switch side of the turn signal relay. When the multi-function switch is triggered to turn the flasher lights on, it closes the circuit. The power can then go through the flasher relay, finally reach the turn signals, and turn them on.

Pretty simple right?

The only tricky thing here is that the turn signal relay, also called a blinker, is not an ordinary one. It doesn’t provide a constant current when the control side of the relay is closed. Instead, this type of relay will alternately open and close the circuit to make the lights blink.

In essence, a turn signal relay works just like any other breaker or thermostatic switch. The heat produced by the current flowing through it will make a metallic strip to change shape. In doing so, it will open the circuit, turning the light bulbs off. As it cools down, the metallic strip will return to its original shape closing back the circuit, making the light turn back on.

The frequency of the blinking is determined by the amount of current consumed by the light bulbs. The higher the current consumption, the slower the blinking goes.

So, why is it blinking faster than it should?

Burnt light bulb

burned out lightbulb

Without a doubt, the most common cause of them all is a burnt light bulb. When any of the turn light bulbs in the circuit burns out or stops working, the flashers will start blinking fast. This is because turn signals operate in pairs.

When the switch is in the “left” position, both the front and rear left turn signals start blinking. The flasher relay is set up to flash at the correct speed while both light bulbs are on and drain a specific amount of current. When one light bulb is burnt, the amount of current drained will change and will cause the relay to flash twice as fast.

Open or short in the wiring

An open circuit on one of the light bulbs will also cause the same condition. A rusted, corroded, torn, or damaged wire can prevent the power from reaching one of the light bulbs. A skinned wire touching the vehicle’s body will create a short to ground causing the exact same problem.

Defective flasher relay

Obviously, a faulty flasher relay or corroded relay pins can either bring your turn lights to flash faster or slower depending on the problem and may also become an intermittent condition. Be aware that this is not a common occurrence. It happens mostly when water is able to reach the fuse box. It causes rust and corrosion to the fuses and relays pins. Water-damaged vehicles are well known for this kind of trouble.

Incorrect light bulb

Replacing a burnt flasher light with a new one of an incorrect wattage will also cause the flasher relay to flash at an incorrect frequency. Higher wattage bulbs will consume more power than what’s prescribed and will change the blinking speed of the flasher relay.

We’ve been seeing a lot of cars coming into the shop lately with turn light problems caused by the owner replacing their light bulbs with LED models. These consumer less power, but make the turn lights go crazy.

Inadequate flasher relay

Most vehicles use a specific flasher relay designed to suit their turn signals configuration. The manufacturer creates a specific flasher relay matching each car specific configuration. They base it on the light bulb’s wattage, the total number of lights flashing at the same time, and the targeted blinking speed. (Some cars have flashing side markers, turn signals on the mirrors, 2 rear turn signals on each side requiring different settings.)

Replacing a flasher relay with a universal one or one coming from another vehicle model or brand will often make the blinking speed change.

For example, some car models may not use the same flasher relay on the sedan, the coupe, and the hatchback model because each one has a different set of tail lights. The hatchback may be equipped with dual turn lights and have a set on the tailgate. As opposed to the sedan which will only have a single set on each corners.

It’s worth mentioning that unless you know for a fact that the flasher relay has just been replaced or you have just bought the car and its maintenance history is unknown, it’s safe to assume that this is probably not your problem.

Incorrect number of lights in the circuit

Once again, this is a problem that we began to see more and more lately. It’s happening with people buying aftermarket parts or installing tons of random bells and whistles to their ride. Adding JDM outside mirrors with amber turn lights will surely give you a lot of street cred. However, omitting to replace your flasher relay with a suitable one will also cause fast or slow blinking problems.

Every time you add a turn light set to your vehicle, the flasher relay should be replaced accordingly. Most speed shops and aftermarket part shop should be able to assist you in finding a relay that suits your needs. If a suitable relay can’t be found, adding a resistance connected in series in your turn signal circuit may help to speed up or slow down the blinking speed. This will bring it back to a normal pace.

General troubleshooting procedure

As with any other electrical problem, the easiest way to find the problem quickly and efficiently is to follow a general troubleshooting procedure. Gradually isolate the problem until you have found the faulty component.

A typical electrical system troubleshooting procedure usually starts with checking the power source, checking the fuses, testing for power at the faulty component’s connector, etc. And that’s what future mechanics learn in school and that’s all right. Following the general procedure will sure get you there but it may take a long time.

Based on my own experience, I know that burnt light bulbs happen a lot more than faulty relays. And burnt fuses won’t make the light bulbs blink faster. A dead battery wouldn’t be able to start the car at all. Instead of blindly following the troubleshooting procedure, we might as well scratch these steps off the list right away and go straight to where the problem may be.

For a quick and easy fast blinking flashers diagnosis, I strongly suggest you follow these steps instead:

1. Check that all turn signals are working

Use the multi-function switch to activate the turn signals on whichever side it’s fast blinking. Make sure that all the turn signals are working. If they are, go to step 4. If they are not got to step 2.

2. Check the faulty light bulb

9 out of 10 times your troubleshooting will stop right there. Simply take out the light bulbs and check if the little wire inside it is broken. A black fog on the bulbs will also indicate it’s not working anymore. Switching the suspected light bulb with a working one from the other side can also help to quickly find out if that’s your problem.

If you need help removing your light bulbs, take a look inside your vehicle’s owner manual for the detailed instructions. On some vehicles, getting access to your light bulbs may be super easy. You may already have enough space to reach it with your hand and take it out. Other cars may require the battery, air filter box, or front bumper to be removed first. Everything will be explained in details in the owner manual.

Once you have confirmed a turn signal light bulb is burnt, replace it with a new one and test it again. If the blinking speed is back to normal, you have found your problem. If not, go to step 3.

3. Check for power and ground to the turn signal

The next thing to check if, your light bulbs look like they are in good working condition, but one is still not lighting up, is if there’s actually a good power and ground coming to the bulb socket. If there’s no power or ground, the light will definitely not light up and will cause a fast blinking condition.

Unplug the turn signal connector and use a test light or a multimeter to test for power and ground in the connector. If power and ground are alright, the light bulb socket may be faulty and you’ll need to replace it. If there’s no power or ground, go to step 4.

4. Test the turn signal relay

If there’s no power coming to the light bulb, it may be because the relay’s control side stopped working and is not making the relay click anymore. If the relay doesn’t click, it won’t supply the light bulbs with the power they need to light up. Takes note that blinkers don’t control each turn signal independently. They power every turn signal of each side at the same time so a faulty relay won’t make the front flasher work while the rear doesn’t.

When a relay is faulty, all left signals or all right signals will stop working altogether. If only one of the left or right signal is working, go to step 6.

test the turn signal relay

If all of the turn signals on one side aren’t working, you’ll need to test the relay. Take it out and test the control side of the relay for continuity. If it’s good, the switch side of the relay will need to be tested next. You can always remove the plastic casing of the relay to manually make it click and test for continuity between the switch side pins.

Another way is to supply the control side of the relay with power and ground by using jumper wires to connect it to a car battery. A bad reading on either of the continuity tests will let you know that the relay needs to be replaced. If everything seems to be in good working order and your turn signals are still blinking too fast, go to step 5.

5. Replace the relay anyway

Auto repair isn’t always an exact science and turn signal relays are often quite inexpensive. It may be a good idea to just replace it and see if it works before going any further.

More recent car models are often equipped with electronic turn signal relays making them harder to test than older models and can also start to freak out for no apparent reason. The next steps will require extensive work. It includes removing trims and larger components. More complicated testing may be needed. Simply try one and see if it works. If it doesn’t, roll up your sleeves and go to step 6.

6. Check for open circuit or short to ground

We already know that your light bulbs are in good working condition and the relay also works.

So, now what?

Well, if the relay is doing its job and is actually sending power to the light and there’s still no power coming to the light bulb’s connector, it can only mean one thing. The wire is either broken or damaged somewhere, preventing the power to reach its destination. And, now starts the hard work.

You’ll have to follow the wire and test it at every connector along the way until you find one with no power. The problem will be located between the last good connector and the first bad one. The wire may have touched a hot part inside the engine bay or maybe rubbed against something and is now burnt or broken.

Squirrels and mice are well known to chew on and cut electrical wires. Rust can also cause wires to break and cause an open circuit condition. Car owners living in a rural area or owning an older vehicle should probably suspect that a little sooner in this procedure.

Newer turn signal systems

All the information included in this article fits particularly well every car models made before 2015-2016. Around that date, cars really took the technological turn and everything became a lot more complicated.

Most recent cars control the lighting system, the power-windows, the power-lock system, and all electrical accessories. It’s done through either a body control module controlling everything or individual modules.

The newer Toyota Prius, for example, may be equipped with over 20 electronic control modules. They control everything from the automatic braking functions, multimedia units, assisted parking features and hybrid and plug-in options. In a vehicle like this, the turn signals will definitely be controlled by some electronic unit and the difficulty level of this troubleshooting will rise exponentially.

Testing control units will require the use of dedicated scan tools and OEM softwares making it hard to diagnose by yourself. Bringing your car to the repair shop and leaving it to the professionals is probably your best bet here.

Because everything is being electronically controlled these days, replacing your turn signals with LED light bulbs may not be a good idea either. If your car is not originally designed to work with LEDs, your lights may start behaving erratically or may not work at all.

The control unit dedicated to the turn signals often receives a signal from the resistance of the light bulb to confirm that it’s working. LEDs have a much lower resistance than regular light bulbs. So, the signal may be out of the normal threshold and may not be picked up correctly by the unit.

On some vehicles, the turn signal may respond in working intermittently or at a different speed than originally intended by the manufacturer. Some units could even think that there’s simply no light bulbs in the socket and, as a result, set up a DTC code and stop sending power to the lights completely.

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