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Headlights dimming when using power windows


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Has anyone else noticed this? At night, with headlights on, if I lower or raise a window, the headlights and panel lights will dim slightly, hardly noticeable but I can see it. If I work the switches two at a time, the effect is a lot more noticeable, nothing shocking like driving with no lights but there is a dimming effect while the motors are working, same goes if I work the switches past the down or up position, as soon as I let go of the switches, the lights go back to normal. I understand the window motors will put load on the electrical system, but shoud it be enough to cause this effect?

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Power windows draw quite a bit of power, so do things such as rear window defoggers and seat warmers. It's normal for things to dim a bit at idle when using these items. The battery is making up for what power the alternator can't produce at low engine rpm. Which is why I don't have the a/c blower set on 4 or the rear defrost on unless I'm moving, it saves the battery and less wear on the alternator.

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I read your post earlier in the day, I had to go out for a bit, so I started playing with my windows, with lights and fogs on, both on the highway, and at idle. I didn't see any variations at all, the interior, and exterior lights remained constant. I hate to be the one to throw a damper on things, but better you get it checked out, in case there is a problem with the charging system.

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Just came back from the dealer, they are telling me this is normal operation, they called the tech center at GM and they where told this is also normal operation. The dealer provided me with a techlink document applicable to all models indicating extra electrical load effects at idle , albeit it is dated 2009. supposedly the alternator regulator on these cars is controlled by the ECM, so it does not excite at a specific RPM as traditional alternators do, this means the alternator is actually not charging all the time at high RPM as in traditional alternator designs, this is done to save fuel. I am not filled with confidence since they told me they no longer test alternators using Snapon D-tac 2, at least I got an incident number out of it.

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  • 4 months later...

I noticed my headlights brighten when taking off from a stop. The ECU should crank up the output on

the alternator to create enough power so you never see it dim.

On my other car (A Honda Fit) had weak starting from new and I found there was a poor connection

from the frame to the engine. I added a 4 gauge wire there and it works great now!

It seems the problem might be that the ECU cannot see the voltage loss creating the dimming. Once

the weather warms up here I can take a look at the situation with the Spark...

Edited by Silver Spark
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