Honda civic 2012 charging battery issue without lights
Honda civic 2012 LX 1.8L won't charge under certain load conditions. Had the
reg/alternator and battery check OK. When the battery is not fully charged and it reads
around 12.3 vdc using a voltmeter across the battery terminals. Leaving the voltmeter
across the battery terminals and the car is started the voltmeter reads around 14.3 vdc
for about 10 seconds. Then the voltage starts to drop down to around 12.3 vdc with the
car running. If the head lights are turned on the voltmeter will then go up to around 14.3
vdc. If driving with the lights on the battery will start to fully charge up. If the car is
driven with the lights off the battery will slowly go dead after several days of starting.
Is this problem a software issue, control module issue, etc.
Sounds like a ecm problem.
So, what's the answer?
This is normal functionality for this car. The ECU throttles back the alternator to save fuel. Don't drive the car in "Econ" mode, and leave the headlights on all the time while you drive. Sounds dumb but it's true.
This is absolutely true. I had exactly the same problem on my 2012 when it was less that 2 years old. The dealership had no idea what was going on. The system limits the output of the alternator when it thinks the battery has enough charge (voltage is high enough). The battery however may lose too much capacity before the charging system recognizes that it needs to recharge it. Turning on the headlights increases the current draw and caused the charging system to recognize that it needs to do its job. The voltage jumps up and the battery is charged. The dealership kept telling me that everything was OK even though there were several time over a couple of months that I had to boost the car. They replaced the alternator even though it tested fine but the problem persisted. They eventually agreed to replace the battery even though it test fine wherever they had it as I had been running with the headlights on keeping it charged. The replacement battery must have had slightly difference characteristics as it worked fine for the few months that I kept the car. My daughters 2013 seems to be developing the same issue. Honda needs to modify their Charging system (ECU) to kick in a little higher voltage. that would allow it to be a bit more tolerant of slight differences between batteries., and probably extend the life of the battery a bit.
I am having the exact same problem with 2012 crv. I replaced battery and alternator. Seems worse in summer months, maybe less lights on.