Turn Signals Work Sometimes? How To Diagnose & Fix

So you went out for a relaxing drive, or maybe you were on the way home when you noticed your turn signals were not working. You might have found yourself telling your significant other they don’t work but they work for them. Heck, you might be trying to figure out how to answer the “you know why I pulled you over” question.

Don’t worry. The case of “my turn signals work sometimes” is a common occurrence but nothing to stress about. It’s usually an inexpensive fix that any of us can handle. Let’s go through some of the reasons a turn signal won’t work and how to fix it.

Blown/Faulty Bulb

The first thing to do is to make sure that the bulb itself is in working condition. If the problem turn signal flickers fast before it stops working, that could mean you just need a new bulb. To check the bulb it’s either under the hood or in the trunk depending on if it’s your front or rear signal. Check the user manual to find it for your specific vehicle.

Once you’ve located the bulb, take it out and shake it to your ear. If it rattles, then it’s time for a new bulb. If it didn’t rattle, then check the connector socket for any signs of scorch marks or imperfections. Now if you happen to have a test light, this would be a good time to use it. With the bulb removed turn your signal on and put the probe from your test light on the power side of the connector, if it lights up then you’ve covered everything under the hood.

Keep that light bulb out for the next step. So what comes next?

bulb socket

Dirty/Oxidized Bulb Socket

What we should always do with any electrical connection is check for any dirt buildup or oxidation. Oxidation, often referred to as electric corrosion happens naturally due to a moisture build-up. That build-up can/will break the power connection between the bulb and socket. It’s an easy problem to fix and even easier to prevent in the future.

While looking into the socket, look at where the bulb would connect to receive power. If the metal tabs look slightly off-color, possibly a green/blue tint, then you’re dealing with an oxidized connection. The best way to go about fixing this problem is by buying a can of electrical cleaner and compressed air from your local auto parts store.

Now before doing any cleaning, you’ll want to disconnect your vehicle’s battery. This will help prevent blowing a fuse and adding more problems. Once the battery is disconnected, simply spray the electrical cleaner into the socket and let it sit for 3-5 minutes, or as long as the directions on the can say.

For good measure, I always spray the can of compressed air into a socket I’m cleaning to push anything out that may have been missed. Now that your socket is clean again, you might be asking yourself “how can I prevent this from happening again?” There is a product many mechanics use called “dielectric grease.”

dielectric grease
Permatex 81150 Dielectric Tune-Up Grease

This product helps insulate electrical connections and keep moisture and dirt out. To apply it, you put the grease on your finger and rub it around the bulb, and put a little dab on the bottom where it connects. Dielectric grease does not conduct electricity so it will not cause any shorts or faults in the connection.

So for this step, all you will need is a good set of eyes, a can of compressed air, electrical cleaner, and dielectric grease. The total should be less than $20. Hopefully, we’re fixed and the turn signals are back to normal. If not, let’s go on to the next step

Blown Fuse

So we’ve done all of our checks under the hood, or the trunk, and we know the bulb is good and the connector is in working order. A blown fuse is where I’d check next because it’s the second easiest fix. Most vehicle fuse boxes are located to the left of the driver floor mat or under the hood near the air filter box.

Check your user manual for vehicle-specific locations as well as fuse identification.

To test a fuse take out your trusty test light and probe both the ground and power connections. If it lights up then the fuse is working as it should. If you don’t have a test light, don’t worry! Pull the fuse and look through to see the “U” shaped metal piece. If that piece is broken, you need a new fuse.

Fuses are readily available and very cheap at any auto parts store. Well, what if we’ve done steps one, two, and three but everything checks out correctly?

Faulty Flasher Module

The flasher module, or commonly referred to as the flasher relay, is how the turn signals work. It’s a bigger fuse that controls the speed and operation of your turn signals.

Pin Electronic Flasher Fix
LED Flasher Relay

Testing a flasher module requires a 12-volt battery, ohmmeter, test light, and a decent amount of electrical knowledge. As a mechanic of close to ten years, I can say testing a flasher module is not worth the time or headache for the low cost of a new one. Flasher modules range anywhere from $10 to $50.

If you think your flasher module is the problem, they’re usually located in the fuse box under the hood. Check your user manual for the specific fuse location. Once you’ve found the flasher module it’s as easy as unplugging the old one and plugging in the new one. If that did not fix your problem, I’m sure the next step will.

Faulty Turn Signal Switch

The turn signal switch is what we want to check last. It’s the most time-consuming fix and if your vehicle is equipped with airbags, it’s potentially a dangerous fix. Please consult your user manual on how to disconnect your airbag for this fix before going any further.

The turn signal switch is the lever we hit up or down to make the turn signals work. It’s not uncommon to have turn signal switch problems. Troubleshooting will require a slight amount of mechanical savvy and a test light.

First, we have to figure out how to get to the back of the turn signal switch. For that, you either remove the top shroud or bottom shroud behind the steering wheel. Once removed, you should see the wires coming out of a box connected to the turn signal lever.

Your user manual should have a diagram of what all the wires control. It’s a simple picture that you don’t have to be an electrician to follow unless it’s a newer vehicle.

Here’s my process that has yet to fail so I know it’ll work for you. A quick tip: I’ll be using the term “back probe” which means sticking the probe from the test light along a wire and jabbing it into where the wire is connected in the socket.

Step 1. Put your right turn signal on

Step 2. Back probe the wire for the right turn signal. Your test light should flash.

Step 3. Back probe the wire for the left turn signal. If your test light flashes then there is a short in one of the wires.

Repeat steps 1-3 with the left turn signal at this time. If the tests show a short in the turn signal switch then replacing the lever should fix your problem!

The Short Version

  • Check to make sure your problem isn’t simply a bulb on its last leg. We occasionally jump the gun and forget about the easy fixes.
  • Clean the bulb socket and add dielectric grease to prevent future problems.
  • Check your fuses! Fuses are always forgotten but in my experience happen to be the culprit often.
  • The flasher module or flasher relay may be the problem. Buy a new one from a local auto parts store and replace it.
  • The turn signal lever switch is the last to check because it can cause the right amount of headaches trying to fix.

Final Notes

The turn signal is a very important element of every vehicle. Even though most people leave a turn signal on for 5 blocks in my neighborhood, I’m glad they’re operational. Hopefully, this guide helped you figure out why your turn signals don’t work, and taught you how to fix it.

For any specific questions on your problems if our guide couldn’t help please reach out and we’ll do our best to lead you in the right direction.