Why your turn signal isn’t working

Your turn signal usually fails due to a burned-out bulb, a blown fuse, a faulty flasher/BCM (body control module), a bad turn-signal switch, or a wiring/ground issue. In many cases, the symptom—fast flash, no flash, or intermittent operation—points directly to the fault. Below is a clear guide to reading the symptoms, the most common causes, and how to diagnose and fix the problem safely.

How to read the symptoms

One side blinks fast or stays on solid

When one side suddenly flashes much faster than normal (hyperflash) or stays solid without blinking, your car is signaling a circuit imbalance—most often a failed bulb or LED mismatch.

• Likely cause: Burned-out turn-signal bulb on that side (front or rear).
• Check: Inspect both front and rear bulbs on the affected side; look for a dark filament or cloudy glass, or test by swapping bulbs.
• If LEDs are installed: The system may detect lower current as a “fault,” causing hyperflash—use vehicle coding (where supported) or add load resistors or the correct LED-compatible flasher.
• Other possibilities: Corroded socket, poor ground, or wrong bulb type (e.g., single vs. dual filament).

Addressing the bulb or correcting the load usually restores normal flash rate; if not, investigate the socket and ground on that side.

Neither side works, but hazards do

If turn signals fail on both sides while hazards still flash, the power and bulbs are likely fine; the fault is typically in the turn-signal switch or related control path.

• Likely cause: Faulty turn-signal/multifunction switch in the steering column.
• Alternative causes: Wiring/connectors between the switch and the BCM; in some models, a hazard-switch internal fault can interrupt the turn circuit even if hazards appear okay.
• Diagnosis tip: If moving the stalk slightly makes the lights flicker, suspect worn switch contacts.

Because hazards work, the flasher function and most bulbs are confirmed; focus on the stalk switch and associated wiring.

Neither turn signals nor hazards work

When all flashing functions are dead, suspect a common power or control component.

• Likely causes: Blown fuse, failed flasher relay (in older vehicles), or a BCM issue (in newer vehicles where the BCM controls flash rate).
• Also check: Battery/charging voltage, main grounds, and trailer modules if equipped.

Start with fuses and relays; if they pass, a scan for BCM faults can quickly pinpoint issues in modern cars.

Dash indicator lights up, but exterior lamps don’t

If the cluster arrow illuminates yet no exterior lamp flashes, you may have localized circuit failures.

• Likely causes: Failed exterior bulbs, corroded sockets, broken ground wires at the lamp assemblies.
• Test: Use a multimeter at the socket; 12 V present with no light points to a bad bulb or ground.

Resolving poor grounds or replacing bulbs/sockets typically restores exterior function while keeping the dash indicator normal.

Intermittent operation

Signals that work sporadically often point to mechanical or environmental issues rather than hard failures.

• Likely causes: Worn stalk switch contacts, loose connectors, moisture in lamp housings, or corroded grounds.
• Road test: Do signals cut out after bumps or during turns? That implicates wiring flex points or the switch.

Systematic inspection of connectors and movement-related wiring can uncover intermittent faults that simple part swaps miss.

After LED or trailer installs

Modifications change circuit load and can confuse factory flash logic.

• LED conversions: Require load resistors or vehicle coding to prevent hyperflash or bulb-out warnings.
• Trailer modules: A faulty or poorly grounded trailer harness can disable or misroute turn signals.

If problems began after mods, revert temporarily to stock or disconnect the trailer module to isolate the issue.

Most common causes

Several failures appear again and again across makes and model years; focusing on these can save time and money.

• Burned-out bulbs: The single most common reason; replace in pairs on the same axle for consistent brightness.
• Blown fuse: Often labeled “TURN,” “SIG,” or “HAZ”; check both cabin and engine-bay fuse boxes.
• Flasher relay failure (older cars): The clicking unit that sets flash rate; modern cars often integrate this function into the BCM.
• Turn-signal/multifunction switch: Mechanical wear causes dead zones or intermittent contact.
• Corroded sockets/connectors: Especially in regions with road salt or after water intrusion in lamp housings.
• Bad grounds: Look for frayed ground straps or rust at lamp assemblies.
• BCM faults/software: Control modules can fail or need reprogramming; fault codes in the BCM can guide diagnosis.
• Wrong bulb type or poor LED retrofit: Mismatch between single/dual-filament bulbs or insufficient load with LEDs.
• Trailer wiring issues: Short circuits or backfeeding through aftermarket harnesses.
• Low system voltage: Weak battery or alternator problems can disrupt flash logic.

If you methodically check these high-probability culprits, you’ll resolve most signal issues without chasing obscure faults.

Step-by-step troubleshooting

Use this practical sequence to locate the fault efficiently, from simplest checks to more advanced tests.

1. Verify symptoms: Left, right, and hazards; note fast flash, no flash, or intermittent behavior.
2. Inspect bulbs: Check all four corners and side repeaters; replace any dark, cloudy, or physically damaged bulbs.
3. Check fuses: Consult the owner’s manual for fuse locations and labels; inspect and replace blown fuses with the correct amperage.
4. Listen for relay click: On older vehicles, the flasher relay should click; no click can indicate a bad relay or no power.
5. Test sockets and grounds: Look for corrosion or melted plastic; clean contacts and ensure ground wires are tight and rust-free.
6. Scan for codes: Use an OBD-II scanner capable of reading body modules; BCM codes can pinpoint circuit faults or switch errors.
7. Probe with a multimeter: Check for 12 V at the socket with the signal on; if power is present but no light, suspect bulb/socket/ground. If no power, work upstream toward the switch/BCM.
8. Evaluate the switch: Wiggle the stalk and see if the signals flicker; if so, the multifunction switch likely needs replacement.
9. Consider modifications: Remove trailer adapters or revert LED conversions to stock to see if normal operation returns.
10. Module/relay replacement: If diagnostics point to the flasher relay (older cars) or BCM (newer cars), follow service procedures; BCM work may require programming by a professional.

Moving from quick visual checks to targeted electrical testing prevents unnecessary parts replacement and speeds a reliable fix.

What it might cost

Repair costs vary by vehicle age and design, with newer cars often integrating functions into control modules.

• Bulbs: $5–$25 each; LED assemblies can be $60–$300 per unit.
• Flasher relay (older vehicles): $15–$60 for the part; minimal labor.
• Multifunction switch: $90–$300 part; $80–$200 labor depending on airbag/trim removal.
• Socket/ground repair: $20–$100 in parts; labor varies with corrosion extent.
• BCM diagnosis/replacement: $150–$400 diagnosis; $300–$900 for module plus programming.
• Load resistors/coding for LEDs: $10–$40 for resistors; $0–$150 for coding at a shop.

Start with the inexpensive, high-likelihood fixes; only move to module replacement after confirming with testing or professional diagnosis.

Prevention and maintenance tips

A few habits can prevent most turn-signal failures and extend component life.

• Replace bulbs in pairs to keep brightness and load balanced.
• Seal or replace leaky lamp housings to prevent corrosion.
• Use dielectric grease lightly on bulb contacts to deter oxidation.
• Choose OEM-spec bulbs or manufacturer-approved LEDs.
• Secure trailer wiring with proper modules and fusing; avoid Scotch-lock taps.
• Check grounds annually, especially in rust-prone regions.

Proactive attention to moisture, corrosion, and correct parts selection eliminates most repeat signal issues.

When to seek professional help

Some symptoms point to deeper electrical or module-level faults best handled with advanced tools.

• Both signals and hazards are inoperative after fuses check out.
• Intermittent issues persist despite bulb/socket/ground repairs.
• BCM-related trouble codes or suspected software issues are present.
• Airbag removal is needed to access the multifunction switch.
• Trailer wiring shorts keep returning or affect multiple lighting circuits.

If you reach this stage, a qualified technician with factory wiring diagrams and scan tools can save time and prevent misdiagnosis.

FAQs

Drivers often ask about safety, legality, and stopgap measures when their turn signals fail.

• Is it legal to drive without turn signals? In most jurisdictions, functioning signals are required; you can be cited if they don’t work.
• Can I use hand signals? Hand signals are legal in many places as a temporary measure, but they’re less visible and not a substitute for repair.
• Will disconnecting the battery help? It may reset a glitchy module but won’t fix a physical fault like a bad bulb or ground.
• Why does my signal click but no lights show? The relay or BCM may be functioning while the lamp circuit is open due to bulb, socket, or ground failure.

Treat workarounds as temporary; prioritize prompt repair to maintain safety and compliance.

Summary

Turn signals typically fail due to a burned bulb, blown fuse, faulty flasher/BCM, worn stalk switch, or wiring/ground issues. Read the symptom—fast flash, no flash, or intermittent—to narrow the cause, then work through bulbs, fuses, sockets/grounds, switch function, and finally control modules. Most fixes are inexpensive and straightforward; persistent or system-wide failures may warrant professional diagnosis.