My friend has a 2010 Civic DX and the left turn signal is causing issues.
The right works just fine, but the left blinks intermittently fast. It will blink correctly for 10-15 seconds, then it will blink fast for 3-5 seconds then back to normal.
Both bulbs work and are blinking at the same rate as each other. This is not a bulb issue, please do not tell me to replace the bulb.
Wondering what would be causing it?
My 3 thoughts:
1. the turn signal switch is going bad. Not sure why it would be only intermittently fast, but it does control the signal.
2. Relay is going bad, again not sure why only intermittently, but it directly controls power to the lights.
3. (not likely) grounding issue, don't think it is this cause even when the car is idle it happens consistently and predictably when the grounding should not be changing.

Anything i missed?
Any thoughts?
Thanks in advance!

 

Which one is it? You said left blinks fast, but then say they both blink at the same time.

 

Its both, the front and rear bulbs on the left side blink intermittently fast but both the front and rear (on that left side) blink at the same rate.

 

Swap bulbs left to right, right to left and see what happens.

 

Thanks for the suggestion, i did so and there was no change.
As mentioned in the original post, this is not a bulb issue.