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Weird Light Dimming Issue while idle


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Just bought a 2012 3.6L AWD SXT
I noticed that while the engine is running and the vehicle is idling with the fan on in the cabin doesn't matter if the AC is on or off. About every 30 seconds the fan speed will slow down and then speed back up and continue doing that until I'm driving again. I checked it at home and saw that why idling, the interior dome light will dim and brighten and well as the headlights, but not the dash or radio. This only happens at idle. Not with the engine off and not while moving. I replaced the alternator and it still happens. I then read it's a bad design with the voltage regulators for these vehicles? And it's normal to happen. I also read it could be a bad battery cell?

Another issue I get is about half the time I go to start I get a long start, with the starter cranking over for about 2-3 seconds before starting. Other times it starts right away? I thought maybe the fuel pump, but I can hear it turn on when I put the car into run.

Any thoughts? Thanks

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Scan for stored codes in ecm. Bad cell stays bad and drops battery voltage. What does multi meter show for volts dc.

 

Load test on battery can be simulated with multi meter and turning on most accessories with car running.

Need to scratch probes on the remote jumper posts to get a good reading.  The  remote contacts drops about 0.3 from main battery posts voltage of 12.7-12.8 for full charged newish battery.

 

Did you add any LED bulbs to the wire harness?

Edited by John/Horace
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I would start with basics...

- Are your battery connections (terminals)  clean and tight

- Were the wires and connections to your alternator inspected and cleaned

- Does your ground wire have a good connection

- And ultimately, is your battery going out

 

My other car just went through this and ultimately the battery was bad. But start with the basics first, then get to testing. 

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What was battery voltage after sitting over night. Around 12.4-12.6 and your battery is probably ok. Maybe unbolt fastners on the remote battery connections and sand until shiny. Add smear of dielectric on surfaces during assembly. My 2014 were pretty dirty when I cleaned them up after alternator replacement. 

 

Was it a new or reman alternator put in. 

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