[DannyV]

Hey everyone, new here! Hoping to get some help.

I have a 2015 Accord 2.4L with 80k miles. The starter was replaced a year ago. Recently, it wouldn’t start, but a jump got it running. After that, it started fine 7-9 times, then died again.

Shops gave mixed diagnoses, two said battery, two said alternator. High tech testers used.

Instead of spending $700+ on an alternator, I bought a Multimeter and tested it myself. Both the battery and alternator read 12.5V (off and on). I also did the old-school test (disconnecting the negative terminal while running), and the car stayed on with no dimming lights. When reconnected, voltage briefly hit 14.5V before dropping back to 12.5V.

I suspected the battery or sensor, so I replaced both. The battery was old and weak anyway, but still, the issue was there.

Then I found something interesting: unplugging the sensors connector made the voltage stay at a steady 14.5V! I drove 7-8 miles, car never died. But because sensor is disconnected, The dash shows a Check Charging System warning.

This is with connector off, Alternator matches voltage. I

This is with connector plugged in, Alternator matches.

I don’t think it’s alternator, but I’m not a mechanic, it may be, I just don’t want to replace if not needed. Voltage is good with connector off. Any idea where the other end of this connection goes? Could there be a fuse or something else to check?

I would do a straight connection but the dash charge error will always be there if I do that, unless there’s a way to bypass? Appreciate any help—thanks in advance!

 

[Glen_T]

Attached is the wiring diagram for the L4 charging system. It looks like there is one fuse that feeds the sensor.

Was the sensor new and OEM? Seems very odd.

Good luck.

 

[DannyV]

Attached is the wiring diagram for the L4 charging system. It looks like there is one fuse that feeds the sensor.

Was the sensor new and OEM? Seems very odd.

Good luck.

Hi Glen, Thx for the diagram. I will check the fuse.

Yes. The sensor I bought is OEM, and in excellent condition. I’ll attach a pic. This one is in mint condition, I might just keep and install this one again because terminal is a lot cleaner.

But either way, the voltage is only good when I disconnect harness from either one.

I tried DL diagram, but it won’t finish. Any info on how to find it?

 

[Ronch]

Did you check the ground connection where black battery cable attaches to the frame? Make sure it's free of corrosion and tight to the frame.

When you tested voltages with engine running, were bright headlights, heater fan and radio all on at same time? The voltage should be ~14.5 volts at battery terminals under those conditions. If not, that would sound -to me- like the alternator is the problem.

In that case, you may want to take it to a shop that can rebuild it for you, probably for a lot less than $700, not including labor if you can't DIY removal/installation....

And read this thread for more info about '15 alternator probs...

 

[mtts60]

The meter testing doesn't really work on newer Hondas due to the dual-mode charging system. The ELD tells the computer to tell the alternator to use low or high-output mode. There was a recall on the ELD, but since you have a new one there it doesn't apply.

 

[DannyV]

Did you check the ground connection where black battery cable attaches to the frame? Make sure it's free of corrosion and tight to the frame.

When you tested voltages with engine running, were bright headlights, heater fan and radio all on at same time? The voltage should be ~14.5 volts at battery terminals under those conditions. If not, that would sound -to me- like the alternator is the problem.

In that case, you may want to take it to a shop that can rebuild it for you, probably for a lot less than $700, not including labor if you can't DIY removal/installation....

And read this thread for more info about '15 alternator probs...

Yep, ground is good And tight. Voltage It’s close, like 14.47 with everything (radio, ac, brights) on. I’m about 85% sure it’s not alternator. If it was, voltage on battery should not jump up after unplugging sensor. The minute I unplug, alternator starts charging the battery. I tried two different sensors. If I could do a straight connect, I would, but Honda won’t allow it, Dash error! It’s gonna take tedious time on my part to figure this out. An electrical tech would probably charge a lot. Just wish I knew where fuse was for this to narrow it down a little more.

 

[DannyV]

The meter testing doesn't really work on newer Hondas due to the dual-mode charging system. The ELD tells the computer to tell the alternator to use low or high-output mode. There was a recall on the ELD, but since you have a new one there it doesn't apply.

The sensor was from a car with 6k miles on it, but if both sensors are bad, which would be a very rare coincidence, why would it charge only after unplugging sensor? By any chance, would you know where the fuses are for this thing? Thx for reply.

 

[DannyV]

This is so strange, tried two different Battery sensors. The only way the battery charges., is if I unplugged the sensor. When unplugged, even with brights, radio, and AC on, battery and alternator are at 14.47 V. Once I plug in the sensor connector, voltage drops to 12.6, just as the battery was before the car started. New battery, new sensor. it’s gotta be the wire, but I don’t know how to check all that. I checked the horn fuse, and the interior light fuse, and the alternator fuse all good. I wish I could just run a straight connection, but everybody says I need this sensor and the dash won’t stop saying check charge system.

 

[Ronch]

The sensor tells the alternator when battery needs charging, and then voltage goes up to ~14.5V. Without the sensor, alternator is constantly charging the battery its max voltage.

Have you checked to see if any OBD codes are stored? If you find DTC P154A, it means "battery sensor internal failure"

And check the part number on both sensors. You want p/n 38920-T2A-A04 (or later). That's the p/n of the replacement sensor listed in Honda's '13-'16 Accord BMS recall.

 

[Glen_T]

Just wish I knew where fuse was for this to narrow it down a little more.

If you look at the wiring diagram, the battery sensor is fed by fuse A20 (7.5A) in the underhood fuse box. But that fuse also feeds several other things like the trunk light, and some interior lights. So worth a check but may be fine.

The Electrical Load Detector (ELD) is in the underhood fuse box. Not sure why it would go bad, but that might be another possibility. It's pretty cheap ($6), so might be worth a try.

Good luck.

 

[DannyV]

Hi Ronch. Thx for reply. So I am attaching pic of both sensors. I also found a very rare tutorial from a guy who shows how to test this exact sensor in ohms. it also tells what the pins and wires are. Pic attached. Maybe you could understand this. I’m going to to try my best. Also, I wonder if Honda will give me a new one of they are bad, since it was recalled.

Link to Tutorial. Hard to understand. Would love any other info. You and google have been a lot of help. The auto places have been horrible trying to sell me a new car basically!

Update: Info - Both sensors are over 1M ohms on pin 2 and 3, the ohms values are very similar on both, ( 1.3M pin2, 1.8M pin3) so that part is fine.


Honda Accord CR2 2013-2019 battey sensor operation and testing | P & G Motors - Seven Hills

pic of both sensors

pic of pins on sensor

 

[DannyV]

UPDATE: I guess after all that happened, I started measuring voltage, which is something I’ve never done with my car. Most cars don’t have the sensor, so the voltage is above 13.5 when idle. I just found out that Hondas with sensor, they will do a low voltage charge at around 12.6-7 when idle, and 14.2/3 when loaded. So all this time, I was good. Not sure if it was the sensor, but I’m leaning towards the battery. The old one has 240 cca left. All this time, I thought my car was messed up, and if I just put a battery and never measured, looks like I would have been fine. I’ll drive it tomorrow and see what happens. But from what I’ve heard, I should be fine. I guess the reason for the sensor is so that the alternator doesn’t have to push to the max if not needed, hence the lower voltage at times. Thx to everyone for all your replies. I’ll leave update after driving a day.

 

[Jammixfuentes]

Because of this, I found the issue of my car.
It was weird because I did not know about smart alternator or whatsoever.
So, when I turn on my lights, the battery starts charging but when I turn it off, the alternator wont charge.
Thankfully I have a battery charging plug where I can monitor my charging.

when I unplugged it, the battery charging functioned to normal level 14.4-14.7

Now I have pinpoint my issue and thanks to this post








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[Accord14']

Wasn’t there a recall on the sensor?

 

[mtts60]

Yes there was.

 

[KW2004Accord]

Wasn’t there a recall on the sensor?

Statement by American Honda Regarding Battery Sensor Recall: 2013-2016 Honda Accord

Honda will voluntarily recall approximately 1.15 million Accord vehicles from the 2013-2016 model-years in the United States to replace the 12-volt battery sensor, free of charge.

hondanews.com