mystery battery light

Ok, so I left my Tacoma parked for 2 months, while I was on a major kayaking expedition. When I came home, the slave cylinder for the clutch had failed, and I repaired that, along with replacing the clutch master cylinder. That went fine, and the clutch feels better than it ever has.

Since then (or maybe since I got back)...the battery indication light has been on in the dash.

Here is what I have already checked:
Battery voltage: 12.5
Voltage when running: 14.0

cleaned and tightened the terminal connections and ground cables.
checked alternator belt for tightness.
checked fuses.


I do not have a CEL light on. No accessories or mods to the electrical system.

So now I'm left with a few possible theories:

Alternator is still bad, even though voltage at battery is OK. Possibly it did not like sitting for 2 months?

I somehow disrupted the battery-light indication system when replacing the clutch master cylinder. I had to remove the fuse/junction block under the dash to replace it. I have double checked my work and everything seems ok.

Any thoughts? Any other tests I should do before thinking about removing the alternator?


Thanks!

 

Look at that



Some of those check probably apply to automotive too.

 

The fault finding chart is interesting (especially because I have an old motorcycle), but I'm not sure how to apply it to the truck situation.

I should also add that I have tried another battery in the truck (mine is the original,7 years old, so possibly on it's way out), but the battery warning light remains on with the other battery.

 

I would take your Tacoma to one of the auto part houses and have them test the battery. Your numbers that you posted shows that the alternator is working. GoodLuck.

 

I ruled out the battery by trying a different battery from my girlfriend's truck...

so in my mind it must be either the alternator or some kind of wiring fault (possibly related to the battery-light sensor)

 

Have you tried disconnecting the battery and just let it sit for 10-15 minutes or however long it takes the ECU to reset? Then reconnect it and start it up.

 

I left the battery disconnected over night last night, with hopes that the ECU would reset and the light would go away....no dice.

 

Either a wiring issue or the alternator as you have tested it with a "Known" good battery. The Battery light is controlled by the regulator circuit in the alternator. I would also recommend that you replace that 7 year old battery.

 

Does anybody know if my voltometer readings can rule out issues with the alternator? When the truck is running, with all the accessories on, I get 13.9 V or so. Would it still be possible to have a bad diode or regulator with that measurement? It seems like the searches I have done reveal a bad alternator in many of these types of cases...

 

Your issue is the fact you left your Tacoma parked for 2 months without someone driving it?

 

hah, it is true. I left it at my parents-in law's house....nobody trustworthy to drive it there

 

Under normal conditions where the wiring was not molested I would say that is the most likely problem ( only because you tested it with a known good battery ). However you also said that you removed the fuse box under the dash and I have no idea what wiring was disturbed in the process.

Have you thought about going to Autozone, Advance Auto or the like and getting them to do a load test on the charging system? It is free.

For the wiring:
A ground downstream of the dash battery light will cause it to illuminate.

For the regulator:
A shorted negative diode will give you a battery light indication with the ignition on.
A shorted positive diode will give you a battery light with the ignition off.

 

After reading some other posts I would like to ask you about the location of the truck while you were gone. Was your truck left outdoors, in a rural area ? You could have been visited by some critter and your wires could have been damaged. I hope this helps Good Luck.

 

I took the truck to a parts store with the alternator battery tester, and all was well. Battery OK, Alternator output OK, Alternator Diodes OK...

So it must be a wiring fault somewhere.



Major lesson learned is to have somebody drive your vehicle if you are going to park it for months. Besides this, my clutch master/slave cylinders and AC compressor have taken a shit since my return.

 

If the ALT is putting out 13.9 with everything on there is nothing wrong with the ALT. 13.9 is more than enough to charge a 12 volt battery. You have a bad battery.

 

I have tried the truck with a battery from a different vehicle, with no change in the warning light. I also just had the truck's battery tested along with the alternator at the parts store.

 

cant help..but a two month kayak trip sound amazing.

 

Have you checked for any signs of a bad or loose fuse?

 

I have looked at many of the fuses, and tested the ones that could be related to the battery light for resistance...they all seem to pass. There are no other electrical issues, so perhaps it is specific to the wire(s) that control the dash light

 

Check the connector that goes into the alternator for corrosion, they grey wire should have output voltage with engine running. That is what sends voltage to turn The light off. If it does not have output voltage the ic regulator has failed