How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Toyotapro Your Own Question
Toyotapro, ASE master tech
Category: Toyota
Satisfied Customers: 9974
Experience:  ASE Certified, 10+ years Lexus and Toyota Certified
Type Your Toyota Question Here...
Toyotapro is online now
A new question is answered every 9 seconds


This answer was rated:


Thank you for using just answer.

Was this an aftermarket alternator or the factory one on the truck? What about the replacement one?

When you put your volt meter on the battery when running is the exact volt reading 15.000 volts?

Any aftermarket equipment on the truck?

Any recent repairs before this issue?

Customer: replied 7 years ago.
it is the stock alt. i bought a new one also from toyota dealer. sometime it shows 15.5 sometimes 16.8 it goes up and down.
Thank you for the reply, please answer all my questions from above so I can best asssit here
Customer: replied 7 years ago.
just a trailer brake but its un hooked.
And did this sudenly appear for no reason or has someone been under the hood recently?
Customer: replied 7 years ago.
no it was setting in drive for a couple days with out driving it i'm the only one in the household.
Does your truck have the optional daytime running lights?
Customer: replied 7 years ago.
yes it does. i cleaned all battery terminals and alt terminals as well.

Have a volt meter handy?

Does this light stay on solid all the time now or does it come and go?

Customer: replied 7 years ago.
yes i have a meter handy. the light comes and goes. also the abs light will come on but not as muchas the battery light. the volt gauge on the dash goes up and down the head lights get real bright and dim.
ok, I have a hunch that the battery you installed might be the issue here, can you get teh light to come on when at idle?
Customer: replied 7 years ago.
the light comes on at idle and even comes on at 3000rpm it seems it does not matter.
ok, start the truck with the engien at idle until the light comes on, then I want you to get an assistant or carefully yourself remove the positive terminal from the battery and tell me if the light goes out.
Customer: replied 7 years ago.
the light was on at idle i removed the positive cable and the light is still on.
ok, shut truck off, have you verified that the wire that bolts to the alternator is clean and tight?
Customer: replied 7 years ago.
yes i cleaned the cable end and both nuts. the nuts are tight. i'm a forktruck mechanic but i can't figure this out.
ok, on the 3 wire connector at the alternator, can you get the volt meter here to see what the voltage reading is on the connector side with the key in the on (not running) position?
Customer: replied 7 years ago.
yes with key on not running one terminal is 11.7 the other 12.0 and the last one 9.3
What is the wire color on the one tha tis 9.3?
Customer: replied 7 years ago.
its white testing 9.6 now.
There is a 7.5 amp fuse labeled ALT-S, what voltage do you read across this fuse?
Customer: replied 7 years ago.
ok, looks like you have a wire issue here, the fuse I mentioned powers the white wire at the alternator for the voltage regulator. If it is only at 9.3 volts it is telling the regulator the voltage is low. This is a solid wire from the fuse block to the alternator so either a junction block issue or a wire issue here.
Customer: replied 7 years ago.
what junction block would it be?

Junction block is another name for a fuse block, what I am teling you here is that you have voltage at the top of this white wire where the fuse powers it but not at the end of the wire where it connects to the alternator, you either need a new fuse block here of the wire is bad somewhere. The alternator and battery you installed are not the issue here.

Toyotapro and 4 other Toyota Specialists are ready to help you

Related Toyota Questions