Rep Power: 0

ok, this may sound stupid, but i think I did it to myself.
car - 2001 honda civic Lx 1.7
this saturday morning, i was trying to investigate a strange rattling sound, coming from left side of engine while cold and disappearing after 15min driving. I was'nt sure if it is from ac or alt pulley or from timing belt area. So i took apart alt belt, started the car. Car started fine, sound was still coming from timing belt cover area, so i found out the source of sound. NOW i put the belt back, tightened it and started the car, car again started fine, ran for 2 seconds, then RPMs dropped and i noticed that battery light was on , on dash board. I knew something wrong with with battery or alternator. I took battery to autozone, they checked battery said it was bad. I got a new battery and came back. I replaced the battery but light was still on. i checked new battery voltage it was 12.6, i started the car, voltage went upto 14.4 or 14.5, then turned on headlights, rear defogger, blower, tape one by one. voltage at bat terminals went down to 12.8, 12.9. I asked someone to rev up the car to 2000 RPMs, voltage came back to 14.2.
then I disconnected the battery while car running, engine went on running, no stopping or stalling.
Finally I checked under hood fuse #9 and under dash 10 & 4. All were ok.
Car now starts and runs fine, with everything working but battery light is on on dashboard. Any suggestion what might be going on.
Is voltage regulator builtin in alternator or is separate than it?
if Multiplex control unit has a DTC stored, can it turn on battery light and not check engine light?

 
Rep Power: 0

I'm no expert, but I had a similar problem. I thought my battery was dead and so I got a new one. Problem was still there. The battery light actually illuminates when there is a problem with the charging system, namely the alternator or a short/open circuit in the system. It does not signify anything pertaining to the battery. Your alternator may be having intermittent problems which points to a failure in the near future.

I replaced my alt with one from Autozone (lifetime warranty) and the light hasn't come on since. The only bad part is this new alternator has a more audible whine to it.

 
Rep Power: 253

I believe the light is on because you ran the car with no alternator belt. Drive it around a bit and it should reset itself.

 
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dissconnect the battery to reset the computer(like 30secs).....if the light comes back on that sounds like what utahbmxer said...alternator is on your way out.

 
Rep Power: 290

Or pull the ECU fuse from the under hood fuse box. That way you get to keep all your head unit settings.

 
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well I disconnected the battery and ecu fuse (#6 underhood) at separate times but of no help. ALso ran diagnostics to find out the alternator control system problem. I mean connections on green 4 point connector going in alternator. they are all fine (black yellow - battery voltage, other 3 wires going to pcm/ecu with no short or open)
after checking all this, again checked the voltage at battery terminals, same original readings, i.e. 14.4-14.7 without any load, 13.1 with all load on, when front rad/ac fan turns on automatically voltage drops to 12.49 but comes back to previous value once that fan turns off.
I just happen to look at battery/alternator test done on my last oil change at Honda Dealer 2 months ago. it said 13.1 volts and says good battery with 440 CC. JUst thinking my old battery might not be as bad i thought. anyway it was a good idea to change that anyway.
Now i plan to go to Dealer / or mechanic for charging system / load test , i might find a free deal if I am lucky. I think DCH Honda near me might do it free.
One thing, Manual says to check for multiplex control unit DTCs. does anyone have an idea, why MCU would turn charging system light on.

 
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Just unhook your battery for about 5-10 minutes, the battery light should turn off. If that's not the case than you might have messed up the computer configuration, what year is your civic? i know the 2000-2001 had this problem, what you need to do is go to the dealer and have them master reset your computer if you have the machine DIY, that should fix the problem other wise your sensor could be shot, or although may sound stupid it happens more often than you think, auto zone may have given you the incorrect battery, make sure it has the required cold cranking amps (refer to manual) if thats not it change the fuse. If that doesnt fix it sorry pal I got nothin lol

 
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I have driven this car for about 300 miles, going and coming back from work everyday, the whole week. everything runs fine including all the accessories. I have an appointment with dealer this Monday, nov 8th. Charging light on instrument panel is still on and it stayed on during the whole week.
Regulator seems ok as when in rev up the car, maximum voltage alternator sends to battery is 14.7.
I was wondering if someone knows how charging light detects that charging system is working ok. If someone could send / post a circuit diagram involving charging light. the circuit diagram from the manual that i have does not include charging light.
thanks !

 
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Derp?

 
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tried / checked all that except going to dealer for master reset. for which i have an appointment on Monday.
what worst can happen if i keep driving the car as it is now ?

 
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civic that derp wasn't for you

 
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Allright ! 2000 miles since that charging light. Car is running fine. Advance auto parts load test revealed nothing wrong i.e. good charging alternator. Charging light still there. Any Ideas ? what can cause charging light other than alternator / ragulator malfunction.

 
Rep Power: 243

If the belt that drives the alternator got adjusted improperly, the charging light will show up also. I think I need Mr. gearbox to verify this one. I read it from somewhere here.

 
Rep Power: 812

its true, the charging light almost never comes on by accident. if its still on, it means something is wrong with the system either the alternator not making enough power, or there is a problem elsewhere in the system. and yes belt adjustment being wrong can cause the light to come on. if its too loose it can slip.

 
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20,000 miles fast forward to today, Charging light still on all the times. the LCD light for mileage went off for couple of months but then came back 7 months ago. A dealer mechanic suggested it that charging light could be due to ELD unit. Is there a way to check if it is the ELD unit causing charging light with no other problem.

 
Rep Power: 812

the check engine light comes on if the ELD is bad. this will usually not affect the charging system. if the belt is too tight, you could have ruined the alternator. also if its not grounded properly, you can have serious issues. if you feel like it, you can bypass the ELD by simply jumpering the connection together after removing the unit. keep in mind this should only be used for testing. leaving the alternator running at full power all the time can greatly reduce its lifespan and will result in worse gas mileage.

 
Rep Power: 0

I know I am waking up an old thread. The above problem (charging light without charging problems) never went away. In meantime, I replaced ELD but it didnt solve the problem. Its been about 45000 miles and 4 years. I have been living with it. Alternator has been charging the battery well and never had a dead battery what makes me believe that its not alternator. Never got it bench tested though but I am planning to do that. Today I was looking through Honda service manual and decided to finally check for the multiplex control system DTCs. When I "shorted" the inspection terminal (I dont have that special tool) and turned the ignition to "II", overhead lights didnt blink or do anything. They were supposed to be "on" for 2 seconds and then blink to show if any codes were stored. Just wondering if anyone else has any thoughts what to do next.
Other things that happened with electrical system in recent past since last post are that odometer light and another speedometer (left half) light was off for about 4-5 months in 2012 but then came back on its own. Now light behind fuel guage and part of speedometer (right half) is off for last 2-3 months. Cruise control is also not turning on at all for last 3-4 months and I still have to troubleshoot that.