2012 Honda Odyssey battery light on

I’ve an Odyssey. the battery is coming on at low RPM below 1500 RPM, “check charging system” message is on the dash. battery light is on idle or stop. when rpm more than 2000, the battery light is off.
I tried to shift the gear on park position, measure the battery is 11.3v, battery light is on, then i increase the rmp to 2000, light dispeared but the votage on the battery is 11.3v and also put the lead on the alternator + , it’s still 11.3v. it seems alternator not output any voltage, but if alternator has no voltage output, how come the battery light will turn off when rpm is over 2000. if the battery light still off no matter what RPM is, I’m sure is the alternator issue. But now the battery light will turn off when RPM over 2000.
I’m confuse whether the alternator regulator is bad or something else cause this problem. any idea?

I would replace the alternator because its not charging the battery. How old is the battery?

Have you considered a belt and/or tensioner problem? Turn the key to the RUN position (engine NOT running) and touch the alternator pulley with a screwdriver tip or even a length of coat hanger. If you can feel a magnetic attraction then the alternator may be fine although this back yard test is not 100% definitive.

Depending upon your tools (if any) you could try to rotate the alternator pulley with a socket or wrench by hand. If the pulley turns somewhat easily then it may be nothing more than a slipping belt.

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What is the battery voltage when the car is not running?

8 yr old car. Battery age? Waiting for OP to say battery is 3 weeks old. But they never mention that. Till you ask them.

We have a 2012 Odyssey, and something very similar happened to us. Turns out it was the alternator.

Cost was about $600 parts and labor. We opted for a Honda OEM, and I recall the generic alternator was maybe $100 less.

Check all grounds before throwing parts.

2 yrs old. battery voltage is 12.4v without running. when engine is running is 11.3v

i want to confirm it’s alternator problem because i throw in a new one has no return. what happen if it end up is other problem.

In the fuse box under the hood, see if the main fuse #1, 125 amp from the alternator to the battery has blown.

I the fuse is fine, then the electrical load detector may be faulty.


Fuse 125A is ok. but i didn’t see the Alternator SP sensor 7.5A fuse.

That fuse is located in the fuse box next to the parking brake pedal.


That fuse is #24 in your vehicle.


#24 is ACG circuit breaker.

Look in the fuse box under the hood.

Fuse #8, 7.5 amp, battery management fuse.


From what you say about the battery voltage it indicates the battery is discharged and needs at least to be recharged using a battery charger. Since the battery warning light goes out when the RPM’s are high it may mean that there are bad diodes inside the alternator. I suspect that is the case here and replacing the alternator will fix you up. The voltage is internal to the alternator though there are other external controls for the alternator. Places like Autozone will test the alternator for free if you can get the car there to have it tested. They can also do an external test of the alternator.

To see if the alternator output wire has any problem with the connection to the battery check the voltage at the battery and then the output lead on the alternator. The voltage should be the same if things are good.

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you are right! I open the back of the alternator, i saw 5 out of 6 diodes base are loose and carbonize. I think i have to buy a new alternator because i saw amazon is selling the dio with $127 when the referbished one just $250. The coil lead connect to the diode socket seems weld on, i have to cut it to get the lead disconnected. don’t know what kind of tool they use to weld it on. also, i tried to solder the diode lead back to the base with lead solder, but it won’t stick to the base, maybe the solder is not hot enough or it need spot welded.

If it were me I wouldn’t bother trying to repair the old unit. I think you are better off and it is more cost effective getting a refurbished unit.

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