What would cause one turn signal to stop working?
A single turn signal stopping is usually due to a bulb or wiring issue on that side. More rarely, a faulty ground, a blown side-specific fuse, or a failing turn-signal switch or relay can be the culprit.
Common causes of a single turn signal failure
Bulb and socket problems
The most frequent reason a single turn signal stops is a burned-out bulb or a poor connection at the bulb socket. Even a bulb that looks fine can fail to make a reliable electrical contact.
- Burned-out or loose turn-signal bulb
- Worn, corroded, or loose bulb socket contacts
- Poor ground or weak electrical connection at the bulb
If the bulb or socket issue is ruled out, move on to wiring and related components to diagnose the fault.
Electrical faults beyond the bulb
Issues in the wiring or related electrical components can prevent one side from signaling even with a good bulb.
- Damaged, frayed, or pinched wiring to the affected side
- Blown fuse for the left or right turn signals (some vehicles use separate fuses)
- Faulty or aging turn-signal relay or control module
Control and signaling components
Less commonly, a fault in the signaling control path can affect just one side, especially in vehicles that use separate modules for left and right signals or a faulty steering-column switch.
- Defective turn-signal switch/stalk in the steering column
- Malfunctioning signaling module or body control module
- Issues with LED drivers or resistors in modern LED turn signals (if applicable)
Step-by-step diagnosis to isolate the fault
The following steps help pinpoint the cause of a single malfunctioning turn signal. Complete these checks safely with the vehicle parked and the ignition off when inspecting components.
- Verify whether hazards on the same side also fail. If hazards do not illuminate on that side, the issue is more likely fuse, relay, or wiring; if hazards work, the problem is more likely the bulb, socket, or switch.
- Replace the suspect bulb with a known-good one to rule out a hidden filament or contact issue.
- Inspect the bulb socket and contacts for corrosion, dirt, or loose connections; clean and reseat the bulb if needed.
- Check the fuse(s) for the turn signals using the vehicle’s manual. Replace any blown fuse with the correct rating and test again.
- Inspect the wiring to the affected side for obvious damage, pinched insulation, or loose harness connections; look for exposed copper or melted insulation.
- Test the ground connection at the bulb socket and along the wiring by ensuring good metallic contact with the chassis; repair as needed.
- Consider the turn-signal switch/stalk: if the other signals from the stalk (like lane-change indicators on the same stalk) are flaky, the switch may be at fault.
- If your vehicle uses a separate relay or driver module for signaling, try swapping in a known-good relay or testing with a diagnostic tool if available.
- For vehicles with LED turn signals, check the LED module/driver and resistors; a failed LED element or driver can cause a single side to fail.
- If the fault remains after these checks, it may require professional diagnostics with wiring schematics and possibly a scan tool.
Following these steps typically reveals whether the issue is electrical, mechanical, or a control component, guiding the repair path.
When to seek professional help
If hazards still work on the other side but the one side remains dark after basic bulb, socket, and fuse checks, consult a mechanic or an automotive electrician. Complex wiring harness tests, module diagnostics, or steering-column work require specialized tools and knowledge. For vehicles with advanced driver-assistance systems, a professional diagnostic approach is often necessary.
Preventive care and quick checks
Regularly inspect turn-signal bulbs and sockets during routine maintenance, especially on older vehicles where corrosion and deteriorating wiring are more common. Keep electrical connections clean and dry, and address any flickering indicators promptly to avoid broader electrical issues.
Summary
A single non-working turn signal is most commonly caused by a burned-out bulb or poor bulb contact, followed by ground, wiring, fuse, or switch issues. A systematic check—starting with the bulb and socket, then fuses and wiring, and finally control modules or switches—usually identifies the fault. If simple checks don’t resolve the problem, professional diagnostics are recommended to safely and accurately fix the signaling system.
