Subaru turn signal blinking fast

What causes a Subaru turn signal blinking fast condition?

Here’s the scoop on a Subaru turn signal blinking fast condition

Back in the old days, mechanical (thermal) flashers would blink fast if a bulb burned out. That’s because a burned out bulb caused less current to flow through the bi-metallic strip in the flasher. So the strip cooled faster and cycled faster.

Well, most late model Subaru vehicles use an electronic flasher relay to switch power on and off to the turn signal bulbs. The electronic flasher monitors current flow to the bulbs. If it detects less current draw, like is present when you have a burned out bulb, it will go into rapid blinking mode.

Why does a Subaru blink fast if the bulb isn’t burned out?

This is what really messes you up. You move the lever and get a turn signal blinking fast condition, but all the bulbs work!! However, if you look closer, you’ll see that one of the fast blinking bulbs isn’t as bright as the same bulb on the opposite side.

Here’s what’s happening:

Car makers can use either two single filament bulbs or one dual filament bulb for their turn signals. In a two single filament bulb setup, one bulb is the parking light and the other bulb is just for the turn signal. In a dual filament bulb, one filament is for the parking light and the other filament is for the turn signal. Subaru uses a dual filament bulb for many of their models.

The filaments in a dual filament bulb each have a different resistance value, so each filament burns at a different brightness. However, if the filament for the turn signal breaks and lands on the filament for the parking lights, the current will still still flow but the total current will be less than the electronic flasher expects to see. It interprets this as a burned out bulb and cycles the flasher much faster. The bulb burns dimly because the brighter filament is shorted to the dimmer filament.

How to fix Subaru turn signal blinking fast

Remove the dimly lit but rapidly blinking bulb. Look for any corrosion on the bulb contacts or in the socket and clean where needed. Install a new bulb. Do NOT automatically replace the $40 flasher relay. It’s almost ALWAYS a bad bulb.

©, 2018 Rick Muscoplat