Flickering Dash and Headlights - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
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post #1 of 2 (permalink) Old 05-20-2018, 12:47 AM Thread Starter
Join Date: Aug 2013
Location: Cleveland
Posts: 13
Flickering Dash and Headlights

My battery light is coming on intermittently and my dash lights and headlights flicker when it does. The car also idles at a higher rpm (around 1100 as opposed to the 750 it usually would) when it does this, which I think means the battery is low. The first thing I tried was replacing the alternator, which stopped the problem for about 3 weeks, but it started again today. I had the battery tested before changing the alternator, and while it was only at about 50% charge it tested okay. All of the connections are nice and tight. Could it be the battery? My mechanic (brother in law, diesel mechanic by trade) is thinking it might be the serpentine belt or the tensioner but he said they both looked fine when we did the alternator.

Also, after the battery light goes back off, the CEL comes on and when I had it checked the code said it was due to low or no power to the knock sensor. I assume this is due to low voltage from the battery, but I have no idea.

Update: just went to Autozone and the battery and alternator are good, but it was throwing code P0621 for generator lamp L control. Could that be the cause of my issue? What are some fixes because google isn’t showing anything.

Last edited by Kilokk; 05-20-2018 at 12:31 PM.
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post #2 of 2 (permalink) Old 05-25-2018, 06:53 PM
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Join Date: Mar 2017
Posts: 66
make sure you have battery voltage at x2 which is for the + battery cable to alternator post (test light on to ground - key off) and then at connector x1 during (key on) make sure you have 5 volts at the grey wire to ground ... if so then get another alternator ... i work for chevy and i went through 3 ac delco remaned alternators to get one that worked properly and if your getting a generic parts store alternator you just never know with parts anymore

Last edited by TCSS07; 05-25-2018 at 07:10 PM.
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