Why are my turn signals flashing at the same time?

Short answer: this usually means the hazard circuit is active or the turn-signal control (stalk switch, relay, or electronic module) has failed, causing power to feed both sides.

In normal operation, left and right turn signals should flash independently when you use the signal stalk. When both sides blink together, it’s a signal that something in the signaling system—ranging from the hazard switch to a wiring fault or a control module—needs attention. This article explains why it happens and how to check it safely.

What this behavior means

When you notice both left and right signals blinking at the same time, it can indicate either the hazard function is engaged or a fault in the signaling circuit is energizing both sides. In older vehicles, a failing flasher relay is a common culprit; in newer cars, the issue is more often a problem with the multifunction switch, the body control module (BCM), or a wiring fault. LED conversions and aftermarket lighting can also confuse the system if proper resistors or wiring aren’t used.

Common causes

The following list covers frequent reasons you might see both sides flashing together. Each item highlights what to look for and quick checks you can perform.

• Hazard switch stuck or hazard relay failing, causing both left and right signals to blink regardless of the stalk position.


• Faulty turn-signal relay or electronic control unit that misbehaves and energizes both circuits simultaneously.


• Defective multifunction switch (the stalk) or its wiring inside the steering column, which can bleed signals to both sides.


• Wiring short or cross-feed between left and right circuits, often from damaged insulation or wear in older vehicles.


• CAN-bus or BCM-related fault in modern vehicles, where a fault in the signaling control logic can manifest as simultaneous flashing.


• Aftermarket LED indicators or other lighting mods without proper load resistors or correct wiring, which can create abnormal signaling behavior.

These causes range from simple to more complex electronics, and the right fix depends on your car’s make and model. If you’re unsure, treat the situation as a safety issue and have the system inspected.

Diagnostic and repair steps

Below are practical steps to diagnose and address the issue. These steps prioritize safety and can often pinpoint whether you can DIY-or-visit a technician.

1. Check whether the hazard lights are functioning. If hazards are ON or cycling regardless of the stalk, the hazard switch or relay is implicated and likely needs inspection or replacement.


2. Inspect fuses related to the turn signals and hazards. Replace any blown fuse with the correct amperage as specified in the owner's manual.


3. Examine both left and right bulbs for damage or burning, and ensure all bulbs are properly seated. Replace any burnt-out bulbs in both sides, since a mis-seated bulb can affect signaling behavior.


4. Test the turn-signal stalk/multifunction switch. If moving the stalk does not yield independent left or right signals, the switch or its wiring may be faulty and require replacement.


5. Check the flasher relay or electronic signaling module. On vehicles with a dedicated relay, swapping it with a known-good unit can confirm a faulty relay. On cars with a BCM, professional diagnostic testing is often required.


6. Look for wiring issues, especially around the steering column and front corners. Loose connections, chafed wires, or recent aftermarket work (like LED upgrades) can cause cross-feed between circuits. Address any damaged wiring or add required resistors/correct wiring for LEDs.

If you do not feel comfortable performing electrical diagnostics or the problem persists after these steps, schedule a professional inspection. Faulty signaling is a safety issue and can be illegal in some jurisdictions if left unresolved.

Additional considerations for modern vehicles

Many newer cars use electronic control modules and CAN bus networks to manage signaling. In these vehicles, a fault in the BCM or a software glitch can cause abnormal flashing patterns that resemble a hardware fault. In such cases, a dealership or qualified auto-electrician with the appropriate diagnostic tool is often required to read fault codes and reprogram or replace the faulty module.

Summary

Turn signals flashing on both sides typically point to a hazard circuit issue or a signaling-system fault—ranging from a stuck hazard switch or faulty relay to a bad stalk, wiring problem, or ECU/module fault. Start by turning off hazards, checking fuses and bulbs, and testing the stalk for independent left/right control. If the issue persists, seek professional diagnosis to ensure safety and compliance.

Why are my blinkers flashing on their own?

That's called hyperflash. It happens when there isn't enough resistance in either circuit (ie a bulb is burnt out). Just replace the bulb(s) and you should be good :)

Why are both my blinkers flashing at the same time?

Both of your blinkers flashing at the same time is most likely caused by a bad turn-signal flasher relay, a short in the wiring, or issues with LED bulbs. A burnt-out bulb on one side can also cause the problem, especially if LED bulbs are installed. To fix it, you should first check for burnt-out bulbs, inspect the flasher relay, and examine the wiring harness and ground connections for any faults.
 
You can watch this video to see a common cause of both blinkers flashing at the same time, and how to diagnose it: 53sNoNonsenseKnowHowYouTube · Feb 9, 2017
Possible causes

• Faulty flasher relay: The flasher relay controls the blinking of both turn signals. If it's malfunctioning, it can cause both sides to flash simultaneously. 
• Burnt-out bulb: A blown bulb on one side of the car can cause both turn signals to flash at the same time, especially if the other side uses low-power LED bulbs. 
• Wiring issues: A short in the wiring harness or a bad ground connection can disrupt the circuit and cause both signals to light up at once. 
• LED bulbs: If you've recently switched to LED turn signals, this can cause the problem. LEDs draw less power, and this can confuse the system, leading to both sides flashing at the same time. 
• Faulty hazard switch: A malfunctioning hazard switch can sometimes be the culprit, as it shares components with the turn signal system. 

This video explains how to diagnose a potential issue with your flasher relay: 42sMaxTheCarGuyYouTube · Jul 17, 2024
How to fix it

1. Check all bulbs: Visually inspect all of your turn signal bulbs (front and back) for any that are burnt out. If you find one, replace it with a new one of the correct wattage. 
2. Replace the flasher relay: The flasher relay is often located under the dashboard. If it's faulty, replacing it will likely solve the problem. You can also try tapping the old one to see if it temporarily fixes the issue. 
3. Inspect wiring and grounds: Check the wiring harness and connectors for any signs of damage, corrosion, or loose connections. Make sure the ground connections for both front and rear turn signals are clean and secure. 
4. Install resistors or a different relay for LEDs: If you've installed LED bulbs, you may need to add resistors to each bulb or install an LED-specific flasher relay to prevent cross-flashing. 

This video demonstrates how to fix hyper flashing in LED turn signals using resistors: 20sTheRetrofitSourceYouTube · Apr 12, 2023

How do you fix hyper flashing blinkers?

So this Tundra's got LED bulbs swapped into its turn signals and they're hyper flashing.

Do all car blinkers blink at the same time?

For new vehicles, there are a few reasons why all indicators aren't the same. Mainly, different cars have different globes and power outputs, which means the power going to the now digitally timed relays can cause the light to flash differently depending on the model.