Battery voltage is critical to keeping today’s vehicles operating correctly. Even a very slight drop can keep you from even starting. SureTrack community member after6tuning had a Kia Soul that wouldn’t start and at first it appeared to be a charging issue. They posed the question to the community, and with the help of fellow community member todawg and others, they were able to resolve the issue quickly.
The following Community Fix summarizes the interaction between members of the community that led to the solution.
2011 Kia Soul Sport 2.0L
No start, replaced door ajar switch.
Car came in on the hook with the battery dead. Customer replaced battery two weeks prior. Charged up and noticed voltage at idle was about 12.8v or so. Put new, not remanufactured 90 amp alternator in and has good voltage until the A/C is turned on with the headlights. When they are turned on, voltage drops to 12.8v, however this is not at first, it takes a moment of running to come down. If you raise the RPMs it immediately goes to normal high 13-14v. I noticed that when I measured voltage at alternator B+ cable it would read about .3v higher than when measured at battery terminals.
Diagnostic Steps Performed/Parts Replaced
Voltage drop at battery cables. Cleaned 2 PCM grounds and battery ground. Positive to alternator voltage drop was excessive at .3v+. Ran brand new 4ga battery cable from battery to fuse box, and fuse box to alternator. Even added additional ground to engine directly from battery. Voltage drops have reduced significantly however the battery voltage measured at the alternator vs the battery posts is about .3v more. So example alternator has 13.1v and the battery measures 12.8v, even with new cable and terminals. Why am I getting .3v less at battery vs alternator. Is it normal for this alternator to only have battery voltage at idle when A/C is on high and headlights on? I thought it should be at least in the 13s.
Best Answer from Community Member todawg
A .3 volt drop is right at the limit. Do a voltage drop test to figure out where the drop is at. Fuse box? Ground? 12.8 volts at idle seems low. The PCM controls the alternator. With a scan tool look to see what the PCM is telling the alternator to do. It normally sends a duty cycle to the alternator.
These alternators are only 90 amp and not very strong, so idling with A/C and headlights on it’s barely charging. Confirmed this by testing another Kia Soul at the local dealer. Now to the original issue that the car came in for which was the battery was dead. Her daytime running lights (DRL) would stay on intermittently causing a drain. I also noticed the interior lights sometimes wouldn’t come on when the driver’s door was opened. I barely touched the driver’s door ajar switch and the interior light came on and the DRL parking lights went off. I got a new switch from Kia and all is well. Customer is happy.
Replaced door ajar switch, charged battery and parasitic draw was eliminated. Customer’s complaint did not return.
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