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Discussion Starter · #1 ·
I have a 2019 EX-L Navi and Res. Recently it has left my wife stranded twice. Tonight she ran in to the grocery store while our daughter waited in the car (likely in ACC mode.)
Vehicle is < 3 years old with 60k miles.
I've tested the battery and it passes load test.
Doing a static draw test, I'm coming up with about 300ma. Have pulled every fuse and relay in the passenger side box with no significant drop. (The PDM fuse did seem to recycle the condition described below. (have not done the other boxes yet due to lack of help)) Here's the strange thing;
If you open and close driver's door the headlamps come on. As soon as they go out, I'll check for draw and it is about 300ma. After 15 seconds or so it drops to about 20-30 ma. After about 30 seconds, it goes back up to 300ma.

Is there a common component that causes this type of condition on a 5th gen?

Thanks!
 

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Many of the systems in the vehicle remain active for several minutes after the car is shut off and the doors are opened/closed.
How are you measuring current draw?
The easiest way I found is to measure the mV drop across the voltage sensor on the negative battery terminal. Put a multimeter lead on each side and turn on the headlights. You should see a voltage drop. There will also be a voltage drop when any circuit is active.

You might already know this, but all of the circuits can be individually tested in minutes without removing a single fuse.
Here's a youtube video explaining how to do this:

 

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Measuring the battery is merely a snapshot in time. I had my dealer test my original battery on my 2018 EX. After three years, the car wouldn't start and yet after driving 20 minutes to the dealer, the battery tested fine. The problem was, the battery was not maintaining its charge. The only solution: replacement.

Bandit400 is right on the money. Like most, I thought I'd get at least 5-7 years out of the battery, like every car I've owned before this one. Nope. These are DC power pigs even when turned off. Honda is still using 1970s battery technology on cars that require far better battery designs. Some members have upgraded to the AGM battery. My service manager said that wouldn't make any difference to the life span, only the extra required draw for the auto-shutoff (or whatever they call it) at stop lights.
 

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Discussion Starter · #4 ·
Many of the systems in the vehicle remain active for several minutes after the car is shut off and the doors are opened/closed.
How are you measuring current draw?
The easiest way I found is to measure the mV drop across the voltage sensor on the negative battery terminal. Put a multimeter lead on each side and turn on the headlights. You should see a voltage drop. There will also be a voltage drop when any circuit is active.

You might already know this, but all of the circuits can be individually tested in minutes without removing a single fuse.
Here's a youtube video explaining how to do this:

Thanks for the reply! I am using a Fluke 23 in series with the negative cable.

Thanks for the video, too! I have been a Harley tech for the last 40 years (and instructor for several of them) and have never seen a voltage drop test used in that manner. I've always used it for checking high resistance. Always good to learn new techniques! I'll have to go through this tonight.

What is bizarre about this situation is that it isn't consistent. It has done it about 4 times since buying the vehicle new. Of course the dealer has never seen or heard of this problem before, ever!

I tested the battery again this morning and it still passes with a 700 amp reading (Matco MD9300 digital tester).

Something else I noticed last night was when I took the fob away from the vehicle, it didn't lock automatically and it didn't beep. Usually does.

Thanks for any and all input!
 

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The correct way to test is by un-plugging the security plug from the hood latch. Then close all doors. Lock the van with the key fob (sets security mode). Wait 20 minutes for all systems to go into sleep mode. Then check draw on the negative cable. Should be below 65 milliamps (mine reads 17).

Every time you open the driver door, it wakes up the various systems, so 300mah may be normal then. I remember mine going from over-200mah, then dropping to 120mah after a minute or so, then dropping to 17mah after 20min. I have no idea how your supposed to pull fuses in the driver's foot well, passengers footwell, or trunk while keeping the ECU in sleep mode. Even having dome lights off still let's some lights come on when you open the doors. Perhaps clamp the door sensors with the doors open, then lock it and wait.

The dealer always goes nuts over anything aftermarket in the car and will blame that (security, led lighting, audio, etc...).
 

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Discussion Starter · #6 ·
The correct way to test is by un-plugging the security plug from the hood latch. Then close all doors. Lock the van with the key fob (sets security mode). Wait 20 minutes for all systems to go into sleep mode. Then check draw on the negative cable. Should be below 65 milliamps (mine reads 17).

Every time you open the driver door, it wakes up the various systems, so 300mah may be normal then. I remember mine going from over-200mah, then dropping to 120mah after a minute or so, then dropping to 17mah after 20min. I have no idea how your supposed to pull fuses in the driver's foot well, passengers footwell, or trunk while keeping the ECU in sleep mode. Even having dome lights off still let's some lights come on when you open the doors. Perhaps clamp the door sensors with the doors open, then lock it and wait.

The dealer always goes nuts over anything aftermarket in the car and will blame that (security, led lighting, audio, etc...).
Thanks for the input! Oh, how I long for times when electrical systems were simpler!
 

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You might come to the same conclusion I did after all of the testing...
The vehicle is chronically undercharging the vehicle due to a defective battery current monitor, which is the device attached to the negative terminal.
This causes low battery issues and premature battery failure.

The part is $90 at the dealership (cheaper online) and takes minutes to swap. I don't know if it can be tested without replacing.
Normally I don't like to guess when troubleshooting, but it seems to have solved our issues.
 

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Discussion Starter · #8 ·
You might come to the same conclusion I did after all of the testing...
The vehicle is chronically undercharging the vehicle due to a defective battery current monitor, which is the device attached to the negative terminal.
This causes low battery issues and premature battery failure.

The part is $90 at the dealership (cheaper online) and takes minutes to swap. I don't know if it can be tested without replacing.
Normally I don't like to guess when troubleshooting, but it seems to have solved our issues.
I don't like guessing either! That's why I'm not jumping to just throw a battery in it before knowing there isn't a problem. Have a part number?
 

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There have been battery complaints ever since this generation van was released. Most people assume the battery is undersized for all of the van's electronics. Some people have upgraded to an AGM battery or larger capacity battery.

I would argue that the battery capacity isn't the issue, the true problem is the battery isn't getting fully charged due to a faulty battery current sensor. Keep in mind that Honda recalled over a million Accords due to this issue.

Simple test: pull into your garage, shut off the engine and check the battery voltage. Compare to the chart below. Leave the hood open and check the voltage in the morning. If the voltage remained the same overnight, then there probably isn't a parasitic drain problem.
Let us know what you find!

Rectangle Font Parallel Symmetry Number
 

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When the vehicle is running, the battery is held at 14 volts. After shutting it off it will take a considerable amount of time for it to come down to it's rest voltage. Also it takes 20 minutes for all the systems to go to sleep and quit drawing down the battery. At least wait an hour before taking your initial reading.
 

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Discussion Starter · #12 ·
Sorry for the lack of recent response. As I originally posted, this is a very intermittent problem. Have not had an issue with it since my original posting. Can't really see a significant draw after the vehicle is parked for a period of time. Charging seems to be correct, at least voltage. Need to find my carbon pile to test the alternator output. Also need to reconfigure the battery cables so I can get an amp clamp on them...

Bandit400, were you able to come up with a part number for the current monitor cable you referred too in an earlier post? Not sure where the other end leads to as it goes into a loom with the positive battery cable. (originates at negative post)

Thanks,
Paul
 

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I don't have the part number, I went to the parts department at Honda and told them what I needed and they gave me the part.

Someone else found the part number on this thread:
battery issues

I can't guarantee that this is the correct part number.

Not sure where the other end leads to as it goes into a loom with the positive battery cable. (originates at negative post)
I hope you aren't touching the positive terminal if you are planning to replace the current sensor. It is attached directly to the negative battery terminal. There is another negative lead two inches away from the battery terminal that needs to be disconnected as well. In addition, there also is a small plug attached.
 

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Just to put this out there, if you cannot find a fused culprit
then the last thing to check is the alternator itself. They all
have 6-rectifier packs in there, and if one comes leaky you
can run current backward from battery through diode to the
case-grounded end(s) of the stator winding(s).

Attach fused 10A meter to both sides of the alt output lug
and then remove the cable from the lug, and see what
reverse current may be flowing. Don't know the spec but
300mA or 30mA would be above it (based on what I see for
other rectifier piece-parts). I wouldn't attach the meter after
disconnect because system inruch current might well pop
the fuse. An alternative might be to first connect (say) a
10-ohm resistor from post to cable, put voltmeter across,
attach cable to see effect (1V per 100mA).
 

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When the vehicle is running, the battery is held at 14 volts. After shutting it off it will take a considerable amount of time for it to come down to it's rest voltage. Also it takes 20 minutes for all the systems to go to sleep and quit drawing down the battery. At least wait an hour before taking your initial reading.
Not that simple. My testing indicates that the ECU charges up the battery to ~14.2V (bulk charge) and apears to hold it there (absorption charge) until the charge current through the sensor @bandit400 mentioned drops down close to ~0A. The ECU then lets the battery voltage drop to 13.2V (float charge). When the vehicle is coasting the ECU will push the voltage back up to ~14.2V. Turning on the headlights will cause the voltage to remain at ~14.0V.
 

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Not that simple. My testing indicates that the ECU charges up the battery to ~14.2V (bulk charge) and apears to hold it there (absorption charge) until the charge current through the sensor @bandit400 mentioned drops down close to ~0A. The ECU then lets the battery voltage drop to 13.2V (float charge). When the vehicle is coasting the ECU will push the voltage back up to ~14.2V. Turning on the headlights will cause the voltage to remain at ~14.0V.
I might be completely wrong about this, but the system voltage while the vehicle is running is basically meaningless.
The part that is missing is how much current (if any) is going to the battery.
If I understand correctly, the battery current monitor is used to measure how much current is leaving the battery. The vehicle adjusts the alternator eddy current to balance out the system. Basically, the alternator is only putting out enough power for the vehicle. However, a defective current monitor results in less power than needed by the vehicle.

I would suggest buying a cheap plug-in cigarette lighter voltage monitor from Amazon, and leaving it plugged in. Instead of starting the vehicle, press the start button without the brake pedal, which puts it in accessory mode. You will know the battery voltage at cold start, after the vehicle has been sitting overnight, etc.
You also could keep track of the voltage when the vehicle was parked for the night versus voltage in the morning to determine if there are any parasitic loads.

Compare with this chart:

Rectangle Font Parallel Symmetry Number
 

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System voltage basically determines if the battery is being charged or not (ie: if current is flowing in or out of the battery). The system/charge voltage needs to be higher than the resting battery voltage plus some in order to drive the chemical reaction in reverse.

Generally speaking 12V (six cell) lead acid batteries need to be charged up to 14.0V~14.4V in order to fully charge, and be "floated" at 13.2V~13.6V to keep them from discharging. If the alternator maintained a system voltage of 12.6V (100% full according to that chart) the battery would never actually charge.

Typically a "smart" charging system will use a current sensor to measure the current into the lead acid battery as it charges it up to ~14.3V. Once the battery is at ~14.3V and the current flowing into the battery drops to ~0A, the charging system assumes the battery is fully charged. At this point it drops the voltage down to ~13.4V to reduce electrolyte loss due to electrolysis - at this voltage there should still be basically no current flow in or out of the battery. The battery should just sit there fully charged as the alternator provides the power for the vehicle. The charging system can use the current sensor to ensure that the battery remains charged (ie: it is not discharging).

So yes, a faulty current sensor will cause the charging system to under- or over-charge the battery.

Judging the state of charge of a lead acid battery using voltage alone is very tricky unless you have a controlled environment. Those voltage/SOC charts are only valid at a specific temperature, and generally require the battery to be completely disconnected from any and all loads.
 

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A thing to note is, system voltage is not battery voltage per se.
There are ohmic drops and there are ground-offsets (like, how
crusty is the alternator-case-to-block-to-battery path?). The
alternators I've had, do their regulating inside the case and
the rest is on you and your hygiene.

Now this shouldn't have to do with discharge, but could have
potential to weaken charging.

Measuring output lug to case voltage, and battery voltage,
you'd hope would return the same result.

Instrumenting them both up, into the cabin with two cheap
DMMs (Harbor Freight has them under $10, sometimes
free coupon, I have about 10 now) might let you see any
"modalities" (like, maybe it charges at cruise but not at idle)
that might lead to "who's bugging?".

I had a Camaro that (as stock) would show volts sagging
and eventually stall at the stoplight on hot days - the stock
tune didn't run fans until some crazy high temperature so
underhood cooked, eventually hitting some sort of thermal
foldback. Fixed that in the fan settings. Too bad no hobbyist
tuning tools for us, on this marque. But scan tool might be
a way to harvest more clues.
 

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Alternator is regulated by ECU in 5th gen vans.

I monitor system voltage via OBD2 port (scantool) regularly when towing as I often charge a trailer battery from the van. That would be over 20,000 kms this year alone - I'm not claiming to have all the answers but I do have a lot of data.
 
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