9thgenidiot

I've read some voltmeter test instructions online but it seems like different sites have different voltage readings to look for.

I put a voltmeter on the neg/pos of my battery today and got the following results:

12.9V: Car OFF, after driving, headlights ran for 2min after I turned off the car to get rid of any "additional" charge
Car jumps to 13.9V: When I turn on the ignition, then drops down to 12.6V and stays there with engine ON, no load
12.6V: Car ON, idling, no load (no radio, A/C, etc.)
13.3-13.9V: Car ON, with the radio, A/C and headlights on
Back down to 12.6V: When I turned off all of the load, engine still ON

Trying to pinpoint a driveability issue and want to eliminate the alternator as the culprit. Thanks for the help.

Car is a 2012 Civic LX

m90polk1

I thought usually when the car is running you should have around 14V when measured at the battery regardless of load from other electrical components.

holmesnmanny

you can safely rule out the alternator being an issue with those results

9thgenidiot

Great thanks guys, on to the next possibility

Calif_Kid

I'm thinking along the same lines as m90polk1 is. I believe that a fully charged battery will read around 12.6V, but after starting the car and the engine idling, you should be reading around 14V. With the reading of 12.6V with the engine idling, but without any other load, sounds like the charging system isn't working correctly. It is interesting that the voltage goes up to 13.3-13.9V with the radio, A/C, and headlights, but still, without a load, it seems like you should be reading well over 12.6V. I'm not sure what the shop manual has for troubleshooting though. - Jim

v4lu3s

i usually follow what the service manual says. i know for my crx 14 volts is not mentioned in it...

Calif_Kid

I included the charging system pages below from my 1996-2000 Civic service manual for testing the alternator and regulator. It looks like with the battery being fully charged, that with the engine at 2000rpm (without a load), if you see over 15.1V, then that is too high, and to replace the voltage regulator. It then checks if the voltage is less than 13.5V, and if it is, then to test and repair the alternator. If all of that is OK, then they then apply a load to get the voltage reading 12-13.5V, and then check to make sure that there are at least 50A. I don't have the tester to check the amperage like they have, but the main thing is that with the battery charged, and the engine running, that a reading of approximately 14V is normal. Anyway, the pages from the shop manual are below. - Jim

holmesnmanny

Honda alternators have two modes, full output and low output when the car is fully warmed up. With no load it will only charge at 12.6 to save gas. When a load is applied it goes into full mode.

Your alternator is doing exactly what it's supposed to do.

If something is wrong with the alternator it will almost always throw the charging system light on.

Calif_Kid

Interesting info. The shop manual for 96-00 Civic mentioned warming up the engine until the fan came on, so wouldn't that mean that the engine is fully warmed up? I've only had a Honda for a few years, and my car is a race car, and my charging light did recently come on, and I ended up having to replace the alternator, so your point about the charging light almost always coming on seems accurate, but still, the way the shop manual is written about testing after the fan comes on, it seems like they are testing with a warmed up (fully warmed up?) engine.

If you're correct about the system charging at only 12.6V when fully warmed up and without a load, then that fits what the OP posted, but still, the shop manual doesn't seem to say that, so just wondering... Are some year Hondas different in this where some charge at 12.6V with no load? OP - what year and model is your car? - Jim

holmesnmanny

I can't say for sure that it applies to every single Honda post 1990 but his tests suggests it applies directly to his car, even though I have no idea exactly what his car is.

With his alternator not loaded it is putting out only 12.6v. With his car loaded it puts out 14 or so. If his alternator was crapping out it would be doing the exact opposite.

holmesnmanny

http://opensiuc.lib.siu.edu/cgi/view...text=auto_pres

9thgenidiot

Thanks for the updates. Reading them all over, the two-mode mention is interesting.. had no clue! That would make sense seeing the 12.6V at idle with no load then.. got a little worried.

Also my car is a 2012 Civic LX, not sure how I forgot to mention that earlier.

My charging light has never come on except for when my original battery died @ 85k miles (currently at 158k, crazy for a 2012 I know).

I am actually thinking my issue could be a sticking EGR valve now (for anyone who may be interested I have a separate thread at https://honda-tech.com/tech-misc-15/...crazy-3255493/).

I'll look over these manual docs, interesting stuff.

Calif_Kid

Really interesting info. Thanks for posting it!! - Jim