I have a 2006 Chevrolet Impala LT, and sometimes the door speakers work, and sometimes they do not. I don't know if it is the speaker cables or in-dash unit that has a problem. What is the best way to troubleshoot and fix this?

Do all of them go out at once? does it matter what you are listening to or driving on a rough road?

It'* just the door speakers. Sometimes one works, sometimes both, but mostly neither work. Usually they just come on while on a smooth highway, but I have noticed them come on going over railroad tracks once, but not consistent.

So it'* just the front door speakers then? The rear deck and tweeters still work?

If I'm reading this correctly, I'd say it'* a loose connection at the BACK of the headunit.

just because its alot more often the speakers go i would try putting different speakers in it from the back if they are the same, i dont know what you have.

Yep the tweeters in the dash and rear speakers always work. I think you are right, most likely wiring / loose connection. It seems like if the amp or speakers had a problem it would either work or not work, but not come on sometimes and go off sometimes.

2006 Impala, everything is stock. 6.5-ish in front doors, 6x9 rear, and tweets in dash

Those speakers have more of a tendency to "blow" than to develop a loose connection/short circuit at them.

The reason I suggested checking the back of the HU is because my 2007 Avalanche had the same problem. The connector on the back of the HU came loose somehow.

k I will check it if I can get back there

It'* a bear, but doable for sure.