vtecnique69

Car: 2008 Civic Si

I might be having an issue with the charging system, but I am led to believe it really is just the battery going south. I tested the charging output of the alternator and I came up with 12.6v at both idle and 3000 rpms, while battery voltage was a measley 10.6v AFTER a long drive and the car off.

So my question is: With a bad battery, will the alternator output drop due to the battery being bad and eating up as much voltage as possible to charge? I always thought it should read 14.6ish volts no matter what. I did read on a forum the Honda ELD will cause it to remain low in a situation such as this.

After the car starts it runs fine, no dimming of lights at all, at idle everything works fine and lights stay bright. This is what makes me think it's all battery issues (well that, and its believed to be an original '08 battery). The only test I did not do is pull the terminals off the battery while the car is running (Rick Spec'd intake, so that would be a pain in the ***).

holmesnmanny

Honda alternators charge in two modes .. low output and high output ... but only when the car is fully warmed up

Low output is 12.60

holmesnmanny

Start the car up cold. Test for voltage. If its not putting out atleast 14 volts with no loads on the alternator is likely bad.

slowcivic2k

If the resting voltage is 10.8, that is the realm of dead cells. Each of the 6 cells put out 2.1 volts of potential. Adding 2.1 volts would make this 12.9, which is very possible after just driving or running the car.

Recharging a battery that cannot take a charge produces waste heat in the diodes and stator of the alternator, which will ruin them. I highly suggest, if you are of limited means, to have the battery load tested at a parts store after a recharge. If your resting voltage is below 11V, you most likely have a shorted plate. Replace it before it ruins your alternator.

fcm

Go to any batt./alt. shop and they will do a free batt. load test and charging system test, it only takes a few min.

With that said, the batt. is old, replace it, life of a lead acid batt. is 5-7 years, your there now. 94

DCFIVER

Turn the high beams and AC on. The charging voltage should go up to 13.5v or higher. Batt voltage after a drive should be around 12.7-12.9v.(key and car off) It should drop down to no lower than 12.5v after 10 mins or so.
WIth a bad battery the PCM will increase the alternator output in order to try to maintain proper sytem voltage. This will stress the alternator and eventually damage it.
Dont ever pull the terminal off of a running vehicle. Besides keeping the battery charged,the alternator prevents transient spikes ,which can quickly damage the pcm and related modules. (Your Civic has several modules)






Just sounds like a bad battery.

vtecnique69

I assumed it was the battery, being the age of it. Replaced it and all is well. Thx!