Check charing system message and battery light on

Sun_odyssey · Aug 7, 2022

Hi my 2012 Honda Odyssey showed "check charging system" message and the red battery light. I found they appeared when the car stopped at the traffic light or speed is low. They disappeared when the car is continuously running at high speed, like 50-60 mile/h. I checked the voltage of the battery. It is 12.66 V when car is not running. It is 14.2 v when car is running at ~1000 rpm without electrical loads, such as AC, radios and headlights. It was 14.3 v when engine runs at 2000-2500 rpm without electrical load. At the full electrical load, the voltage drops to 12.8 v.

I found the alternator is somehow still charging the battery. Because I left the car in the garage for two weeks, when I came back to start the car, The battery was low and the car just barely started. But after I had the car run for 15 minutes, I shut off the car and restarted, I could start the car much faster.

So is the alternator bad? or something else is bad? Please help and share your opinions.

WiiMaster · Aug 7, 2022

Check the spool valve above the alternator for leaking oil.

Sun_odyssey · Aug 8, 2022

Oh, I forgot to mention that in May the van had a "check engine" light on, I had the Honda dealer checked and fixed. They found leak on valve cover gaskets and replaced it. Is it possible that the leak on Valve cover gasket damaged the alternator or their repair messed up the alternator? The van has only 81K miles. The battery is less than 2 years old.

DanW · Aug 7, 2022

I would get the battery load tested. Just because the battery has good voltage doesn't mean it has enough cranking amp to start the van. Also it would be nice to know how old the battery is and the mileage on the van.

Sun_odyssey · Aug 8, 2022

Thanks. I can start the van, just don't know what causes the "check charging system and red battery sign". The van has only 81K miles. The battery is less than 2 years old.

DanW · Aug 8, 2022

The oil from a leaking valve cover gasket could have dripped down on the alternator and damaged it but you said it was reading 14.2 volts while the car was running which is normal. Did the dealer replace the spool valve mentioned in the above post? The spool valve is just above the dip stick and has been known to leak oil down on the alternator and kill it. I would still check the battery and eliminate that possibility, even after sitting for two weeks the battery should turn over the engine easily.

Sun_odyssey · Aug 10, 2022

thanks for all your comments. Yesterday I went to auto zone to check the battery and alternator. They said the alternator is good. When they tested the battery, it shows "good", but only has 60%, and then they charged the battery. It took two hours to charge it to 82%, so they told me the battery needs to be watched. This morning, I went to auto zone again. the battery dropped to 50% overnight. So it seems that something drains the battery, or the battery does not hold the charge? Since my battery is still in warranty, I went to Walmart. They tested it, and the meter showed it is good, so they don't replace it. I will have a 8 hour-trip next week. Is this van reliable to drive? Or at least I need to replace a new battery? Thanks for all you comments!

WiiMaster · Aug 10, 2022

Do a parasitic draw test.

Sun_odyssey · Aug 10, 2022

Yes, it is probably parasitic draw, because after the battery was charged to 82% yesterday, i took it back to my house and installed it in the van. Then this morning I drove the van to autozone for alternator test. Autozone was just a few minutes away (less than a mile) from my house. I doubt that short distance driving could get the battery drop from 82% to 50%. The van has a backup camera with two signal transmitters that i installed miserly 10 years ago. I believe the two transmitters are constantly using the battery even when the van is parked in garage. But they never caused any problem over the past ten years. I could not think of anything that could drain the battery overnight. I will do a parasitic draw test tonight.

Sun_odyssey · Aug 10, 2022

one more question: Even if there was a parasItic drain, can it trigger “check charing system” and “red battery”?

DanW · Aug 10, 2022

Why not charge the battery disconnect it from the van and let it sit overnight to see if it holds the charge. If it doesn't you know its the battery. If it does you know you have a parasitic draw.

Sun_odyssey · Aug 12, 2022

I did the test as you recommended. I disconnect the battery at the night of August 10 till today. I measured the voltage on the yesterday's morning and this morning. Here is the result: the voltage starts with 12.51. On yesterday's morning it dropped to 12.48, and this morning it was 12.46. Obviously, it slowly drains itself overtime, but I am not sure it is a normal drain or a significant drain. Any experience on it? I will do a parasitic draw test by measuring the current today and post the result here. Thanks!

THE ELITE · Aug 11, 2022

Hello i'm new here for the past year and a half i've been having the same issues with alternator. I had changed around 5/6 of them . I even tried the Denso brand but I still got the same message on dashboard? check charging system . Took it to an electrical shop / mechanic said that the ECM was good and changed the alternator. 3 months later same issue . This is frustrating . Any suggestions would be helpful .

phattyduck · Aug 11, 2022

Any oil leaks on the alternator? The battery sensor may also go bad or there could be other wiring issues.

-Charlie

THE ELITE · Aug 11, 2022

No oil leaks on alt.

Sun_odyssey · Aug 12, 2022

Here is the update: my multimeter does not have 10 AMP for parasitic draw test, so I found on website a protocol to test alternator (below):
How to test the alternator
The easiest method to check the alternator is by measuring the voltage at the battery terminals when the engine is running.

Start your Odyssey.
Connect the black cable of the multimeter to negative terminal of the battery, and the red cable to the positive terminal.
The voltage should be between 13.5 and 14.8 volts with the engine running. (My battery is 14.3 v)
Switch on the accessories in your Odyssey, for example, headlights, AC fan at full speed, and interior lights.
The voltage should remain around 14 volts. If it drops and remain below 13.5 volts, it indicates a problem with the current supply from the alternator. (My battery started with 14.03 v and slowly dropped to 12.08 v and seems to be stable there. When I turned off all the accessories, it came back to 14 v.)
If the voltage drops below 12 volts with the engine running and the accessories turned on, it means the current supply from the alternator is completely cut off and all the electronics are solely powered by the battery.

The conclusion based on this test: the alternator is not completely bad, but intermittent bad. Is that right? Is the method reliable?

oldskewel · Aug 13, 2022

your post prior to this one suggests your battery is OK.

Sun_odyssey said:
Here is the update: my multimeter does not have 10 AMP for parasitic draw test,

Even if you had one with 10A, there would be a good chance it would blow the fuse during the current surge when the car powers up after reconnecting the battery circuit. Measuring current on cars can be difficult. Many cool ways to do it though. My favorite is with a DC clamp meter. You clamp it around one of the battery cables and it measures current based on the induced magnetic field. There is no way to blow any fuse in that. For chasing a parasitic draw, best would be a pretty small unit, maxing out at around 100A, with a small clamp.

Sun_odyssey said:
so I found on website a protocol to test alternator (below):
How to test the alternator
The easiest method to check the alternator is by measuring the voltage at the battery terminals when the engine is running.

Start your Odyssey.

Connect the black cable of the multimeter to negative terminal of the battery, and the red cable to the positive terminal.

The voltage should be between 13.5 and 14.8 volts with the engine running. (My battery is 14.3 v)

Switch on the accessories in your Odyssey, for example, headlights, AC fan at full speed, and interior lights.

The voltage should remain around 14 volts. If it drops and remain below 13.5 volts, it indicates a problem with the current supply from the alternator. (My battery started with 14.03 v and slowly dropped to 12.08 v and seems to be stable there. When I turned off all the accessories, it came back to 14 v.)

If the voltage drops below 12 volts with the engine running and the accessories turned on, it means the current supply from the alternator is completely cut off and all the electronics are solely powered by the battery.

The conclusion based on this test: the alternator is not completely bad, but intermittent bad. Is that right? Is the method reliable?

This definitely sounds like something is wrong with the alternator. If it is repeatable (i.e., you can repeat that careful test with identical results), I would not call it intermittent, but that is just terminology. The difference there is that if something is intermittent, I think of the failure as being GONE, not just undetected; in your case (if it is as you think), the fault (that voltage drops when loaded, after a while) is always present, just only detected under certain conditions. But it does sound like something an in-store bench test might miss.

Honda's ELD - Electric Load Detector - system is supposed to reduce alternator output in certain situations, when power is not needed and the purpose is to be more fuel efficient. But that would not make sense in this case unless the logic (it is PCM / ECU controlled, like most things) is broken, since when power demand increases, the alternator should not be throttling back.

On most cars there is a way to bypass the ECU's charging control - making the alternator charge at all times. Like back in the good old days, when if the engine was turning, the voltage regulator would be controlling the field current to hold system voltage steady at 14.4V. So reliable, and maybe slightly inefficient once in a long while.

If you're looking for a quick solution, I'd just replace or repair the alternator. If you really want to try harder on the diagnosis, I'd see if you can figure out how to hot-wire the charging control, and repeat your test to see if it holds or drops voltage. It could be that you just need to set a wire to ground or B+, or it could be that you need to set a pulse width modulated 5V signal.

And if you do take the alternator out, I'd just then start carefully taking it apart and observing. Oil? Debris? Loose screws? Loose 4P connector or B+ wire? Worn out brushes? Loose screws after the cover is off? Then there are a series of electrical tests you can do on it. I've posted a few times on this forum on alternator repairs, so if you search with my name, you should find some info.

DanW · Aug 12, 2022

Not sure but it sounds like a bad voltage regulator which is part of the alternator. Not sure why they could not find that out when you had them check it at the auto parts store.

phattyduck · Aug 12, 2022

Load on the test might not be enough to stress the alternator enough. I would guess a bad diode, not regulator (the regulator seems to be working when there isn't much load). That could also explain the parasitic draw.

-Charlie

WiiMaster · Aug 12, 2022

Hondas do have dual stage charging so the drop you're seeing could be low charge mode?

phattyduck · Aug 12, 2022

Low charge mode should never happen if the headlights are on or AC is on.

-Charlie

oldskewel · Aug 13, 2022

Yes, you are right that having the voltage increase from 12.3 to 12.6 at the end means the alternator was doing some charging. Risky to drive it that far with the charging light on - if it had truly not been charging at all, a battery would probably have run down low enough to stop the engine.

When I had the problems discussed in the link back in post #9 above, I quickly installed a digital voltage gauge so I could confirm to myself (and my wife when she was driving) whether things were charging, even when the light was on.

Before installing that, I used a little eBay gauge plugged into the power outlet. If you have neither of those, but do have an OBDII reader, you may be able to read system voltage on that, as a live reassuring measurement that things are OK and not about to die (as you drop to about 10V, probably).

I doubt you would find a pro who would disassemble and troubleshoot the alternator after removing it. You might find an alternator rebuild shop to do that, and maybe the pro would send it there.

But at that point, once you have pro's involved, they'd probably just want to do a replacement, which I think would be a fine decision for you.

I can't speak from experience since I have never bought a Honda replacement alternator, but there is are a lot of stories on here about people having their replacement alternator fail before too long, when it was not a new Denso (the OE supplier on your car) or a Denso-rebuilt Denso. So I would go for a Denso.

To be clear, a Neverlast branded rebuild of a Denso alternator would not be likely to last long, yet the guy at the parts counter or service desk might assure you it is a Denso.

Your logic and care in measurements and observations gives me confidence that you would be able to figure out what is going on with the old alternator once you got it out. Some people seem to think electrical stuff is black magic, but I'd say that opening up the alternator is a small fraction of the difficulty of removing it from the car, and even that is pretty easy for some people (but apparently difficult for many).

Sun_odyssey · Aug 13, 2022

oldskewel said:
Yes, you are right that having the voltage increase from 12.3 to 12.6 at the end means the alternator was doing some charging. Risky to drive it that far with the charging light on - if it had truly not been charging at all, a battery would probably have run down low enough to stop the engine.

When I had the problems discussed in the link back in post #9 above, I quickly installed a digital voltage gauge so I could confirm to myself (and my wife when she was driving) whether things were charging, even when the light was on.

Before installing that, I used a little eBay gauge plugged into the power outlet. If you have neither of those, but do have an OBDII reader, you may be able to read system voltage on that, as a live reassuring measurement that things are OK and not about to die (as you drop to about 10V, probably).

I doubt you would find a pro who would disassemble and troubleshoot the alternator after removing it. You might find an alternator rebuild shop to do that, and maybe the pro would send it there.

But at that point, once you have pro's involved, they'd probably just want to do a replacement, which I think would be a fine decision for you.

I can't speak from experience since I have never bought a Honda replacement alternator, but there is are a lot of stories on here about people having their replacement alternator fail before too long, when it was not a new Denso (the OE supplier on your car) or a Denso-rebuilt Denso. So I would go for a Denso.

To be clear, a Neverlast branded rebuild of a Denso alternator would not be likely to last long, yet the guy at the parts counter or service desk might assure you it is a Denso.

Your logic and care in measurements and observations gives me confidence that you would be able to figure out what is going on with the old alternator once you got it out. Some people seem to think electrical stuff is black magic, but I'd say that opening up the alternator is a small fraction of the difficulty of removing it from the car, and even that is pretty easy for some people (but apparently difficult for many).

I just ordered a digital Voltmeter. It is a good idea to monitor the real-time voltage while driving. In the mean time, I will try to find out what is the problem. I have read the link you provided which is very informative. I will see what i can do to find out and post the result here to share. Thanks a lot for all the suggestions.

Check charing system message and battery light on

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