Disabling Smart Alternator on 2019 Sentra ?

[SwampSurvivor]

Wondering if anyone here has any actual info on it. I keep reading about "depinning" an alternator connector to force it to do normal alternator systems. I have been planning on doing it for a while.

Went to drive the car to work today and it would barely crank and not enough to start. Battery was sitting at 12 volts. The other day I moved it into the garage to get it out of the hail and noticed it cranking slowly. Then last night I moved it out of the garage to work on the mower and it seemed to crank slower. In hindsight I should have let it run longer.

We have been short tripping the Sentra back and forth to my mom's, about 2 miles round trip. The trip there is uphill and I'm on the throttle which "shuts off" the alternator. The trip back is mostly downhill so it's coasting and charging. Probably not enough.

This happened over last summer and I assumed it was the battery so I replaced it with the "bigger" battery available for this car. I then proceeded to use that battery over the winter running a winch and lights on my 4 wheeler without issue ...

I don't think it's a draw because it can sit a month or more at a time and be fine. It appears to just be from short tripping and the "smart" alternator.

If anyone has access to a wiring diagram that would be great!

 

[AZjeff]

How close are you to Eric O? He knows automotive electronics.

 

[cptbarkey]

12 volts is a dead battery. Get a new one.

 

[supton]

Are you sure its cutting the alternator under throttle? I'd think the systems would want more voltage not less.

Do you have a voltmeter that you can leave hooked up? Might need a relay controlled by switched 12V so as to disconnect when not in use. But once done, maybe you could "fix" the problem by leaving the headlights on whenever driving--maybe that would force the alternator to run more aggressively.

Lastly, like cptbarkey says, 12V is low--maybe you just have a bad battery.

 

[zzyzzx]

Get something like this:
https://www.amazon.com/INNOVA-3721-Battery-Charging-Monitor/dp/B000EVWDU0/
And a battery tender. You need both.

 

[Doc8404]

Is it like the Ford Battery Management System?

Ford has a plug near the negative cable you can disconnect.

 

[SwampSurvivor]

12 volts is a dead battery. Get a new one.

It's only 9 months old.

Are you sure its cutting the alternator under throttle? I'd think the systems would want more voltage not less.

Do you have a voltmeter that you can leave hooked up? Might need a relay controlled by switched 12V so as to disconnect when not in use. But once done, maybe you could "fix" the problem by leaving the headlights on whenever driving--maybe that would force the alternator to run more aggressively.

Lastly, like cptbarkey says, 12V is low--maybe you just have a bad battery.

This is an issue we've had with this car since it. When we first got it , it sat a lot and I can remember the blower slowing down when getting on the gas the blower would slow down. I hooked up a meter to the battery tender leads I have in the cabin and it'll drop down to 12.2 or 3 while cruising then bump back up to >14 or so when off the gas.

Idling in park it's always >14V

 

[Sayjac]

Before I would mess with the alternator, I'd put the battery on a good maintainer and charge it back up regularly. That's a procedure I try to do with all my vehicle batteries. In my case I use a NoCo Genius2 amp charger/maintainer.

 

[walterjay]

Also consider a small solar charger that plugs into the cigarette lighter or usb. I use one and alternate it on seldom used tractors and truck. Works great.

 

[supton]

This is an issue we've had with this car since it. When we first got it , it sat a lot and I can remember the blower slowing down when getting on the gas the blower would slow down. I hooked up a meter to the battery tender leads I have in the cabin and it'll drop down to 12.2 or 3 while cruising then bump back up to >14 or so when off the gas.

Idling in park it's always >14V

That just seems strange to me, like not normal. Maybe it is but still.

In the end, charger and/or longer trips, it's what would have been recommended before any kind of smart alternators were the rage.

 

[SwampSurvivor]

Before I would mess with the alternator, I'd put the battery on a good maintainer and charge it back up regularly. That's a procedure I try to do with all my vehicle batteries. In my case I use a NoCo Genius2 amp charger/maintainer.

I made a quick disconnect battery maintainer for it a few years ago. I'll probably leave it on that over the weekend.

Also consider a small solar charger that plugs into the cigarette lighter or usb. I use one and alternate it on seldom used tractors and truck. Works great.

Unfortunately the power outlets all shut off with the ignition but I do have a few solar chargers with the same connector as the quick connect battery maintainer.

 

[Chris142]

Put your volt meter leads on + and - and drive the car. While that won't tell you amps it will tell you if it's charging enough to charge the battery.

 

[IndyIan]

Do you have a scangauge or ultragauge, I find its reading of ECU voltage is right on with the battery voltage, then you can see in real time what's going on. Some cars use intake air temps to determine ideal alternator voltage.

Do some reading on how the Sentra ECU is supposed to run the alternator, and also if there is a default mode. On my Focus I've read that if you unplug the 3 pin control plug, the alternator will just go into "safe mode" and outputs 13.8v steady, which sounds not bad to me.

Right now I have the opposite problem, alternator voltage output is perfect at all rpms and temperatures, except when the car is warmed up above 160F water temp, and at 800rpm idle, then the ECU shuts the alternator off totally... Turns it back on at 900rpm and above.

Charge your battery up though at home, my healthy fresh charged 40r battery could easily run my car for 45 minutes(with minimal elec. loads) to get to work. Only down to 11.9-12v. Then I charged at work and drove home. Did that for 2 days before I got my rebuilt one back.

 

[SwampSurvivor]

Put your volt meter leads on + and - and drive the car. While that won't tell you amps it will tell you if it's charging enough to charge the battery.

I've driven around with the meter plugged into my quick disconnect port for the battery maintainer. We never had a battery go flat back then but that was during the 'vid and the car just sat. So I had it plugged into a battery maintainer. Driving around on the throttle, it would drop to low 12s (12.2-12.3) then off it would shoot back up above 14. Same sitting at lights, it would be above 14 or if I was at the end of a longer drive it would be higher 13s which seems normal.

Do you have a scangauge or ultragauge, I find its reading of ECU voltage is right on with the battery voltage, then you can see in real time what's going on. Some cars use intake air temps to determine ideal alternator voltage.

Do some reading on how the Sentra ECU is supposed to run the alternator, and also if there is a default mode. On my Focus I've read that if you unplug the 3 pin control plug, the alternator will just go into "safe mode" and outputs 13.8v steady, which sounds not bad to me.

Right now I have the opposite problem, alternator voltage output is perfect at all rpms and temperatures, except when the car is warmed up above 160F water temp, and at 800rpm idle, then the ECU shuts the alternator off totally... Turns it back on at 900rpm and above.

Charge your battery up though at home, my healthy fresh charged 40r battery could easily run my car for 45 minutes(with minimal elec. loads) to get to work. Only down to 11.9-12v. Then I charged at work and drove home. Did that for 2 days before I got my rebuilt one back.

I do have a BT OBDII scanner that could do it. I'm wondering if that's seeing different voltage than what I'm seeing directly on the battery? I'm sure that could cause issues. I have used a multimeter connected directly to the battery while driving and it's definitely doing smart "dumb" alternator things.

As I learned in the past, my Jeep will run 90 minutes with no alternator

 

[IndyIan]

I've driven around with the meter plugged into my quick disconnect port for the battery maintainer. We never had a battery go flat back then but that was during the 'vid and the car just sat. So I had it plugged into a battery maintainer. Driving around on the throttle, it would drop to low 12s (12.2-12.3) then off it would shoot back up above 14. Same sitting at lights, it would be above 14 or if I was at the end of a longer drive it would be higher 13s which seems normal.



I do have a BT OBDII scanner that could do it. I'm wondering if that's seeing different voltage than what I'm seeing directly on the battery? I'm sure that could cause issues. I have used a multimeter connected directly to the battery while driving and it's definitely doing smart "dumb" alternator things.

As I learned in the past, my Jeep will run 90 minutes with no alternator

I guess if your BT OBD2 scanner is seeing different voltage than your multimeter, then you've got one thing to fix and see if it helps, as the ECU needs to read the correct voltage.

I have my ultragauge set up with an alarm for low voltage 12.8V(alternator is off) and high 14.9v which is useful as sometimes when my alternator is turning back on, coming off of idle, it must get told to go full charge field and hits 15.1 for less than a second, as the screen doesn't show it, but the alarm displays what the peak was.

But it seems like your alternator is fine, just getting told to do dumb things.... Maybe this will help you?

He did one on the Ford system that my car uses.

 

[zzyzzx]

As I learned in the past, my Jeep will run 90 minutes with no alternator

I usually only got around 30 minutes.

 

[Bottom_Feeder]

Driving with the headlights on all the time keeps the alternator in my Accord always in 'charging mode' or whatever. Testing with a voltmeter when it's running you can see the alternator output jump to over 14 volts when the headlights are switched on. Same with the AC.

 

[meep]

This really isn’t a BMS problem, and undoing that isn’t going to solve it - it’s simply that the drive cycle is too short. I had a similar routine for a spell prior to the days of BMS and had to run a charger. It takes *time*, not just volts, to charge a battery. NOCO 5 amp FTW!

 

[SC Maintenance]

I doubt its your smart charge system. I disabled both my Nissan's - and the batteries do last a little longer, but its not a cure all. Its really not all that "smart". It cuts off the charge when it thinks your battery is fully charged, and there is low current draw. Otherwise its pretty much normal - but there is no "float" charge which is sort of a problem.

I would get your battery tested first. If it is fine - then put it on a float charger, as your starting point.

If you still want to disable, the simple way on older Nissan's at least is usually just to disconnect the battery current sensor - its on or near the negative terminal. If its like most Nissan's - that will just put it into dumb alternator mode. You might get a code - I did, but I cleared it and it has never come back?

I would also just monitor things with something like a cigarette lighter voltage meter - there cheap on amazon or wherever, and see what it is doing.

Another question - do you have any aftermarket electronics. People will install accessories on Nissan's and home-run the ground, which bypasses the current sensor for that load - which can cause undercharging as well.

 

[SwampSurvivor]

I doubt its your smart charge system. I disabled both my Nissan's - and the batteries do last a little longer, but its not a cure all. Its really not all that "smart". It cuts off the charge when it thinks your battery is fully charged, and there is low current draw. Otherwise its pretty much normal - but there is no "float" charge which is sort of a problem.

I would get your battery tested first. If it is fine - then put it on a float charger, as your starting point.

If you still want to disable, the simple way on older Nissan's at least is usually just to disconnect the battery current sensor - its on or near the negative terminal. If its like most Nissan's - that will just put it into dumb alternator mode. You might get a code - I did, but I cleared it and it has never come back?

I would also just monitor things with something like a cigarette lighter voltage meter - there cheap on amazon or wherever, and see what it is doing.

Another question - do you have any aftermarket electronics. People will install accessories on Nissan's and home-run the ground, which bypasses the current sensor for that load - which can cause undercharging as well.

It's 100% from being short tripped. It can sit a month and be fine. But we've been driving it just around town in a manner where it doesn't charge for more than 3 or 4 minutes.

I found the plug, looks like ours does have the easy way to do it. I think I'm going to disconnect it and monitor voltage.

If it's going to be pushing 14.4 volts when it's 95 degrees out, I'll have to plug it back in. Don't want to explode a battery.

The only aftermarket thing electronically on the car was the battery tender which I had wired to the battery with a quick disconnect, but I removed that when we put in a new battery in August.