Alternator charging problems?

Wathen316Uk

New member
Joined
Mar 21, 2016
Location
UK
TDI
VW Jetta 2006 1.9 TDI
I've got a 2012 VW Passat Bluemotion purchased in February 2017. I bought one of those gadgets that fits cigarette lighter to show what battery is charging at when I had issues with my Jetta. I've used it over last few weeks to check all is ok. Recently it seems to charge at 12.7 whenever I am driving normally. If driving downhill or with foot off accelerator it creeps back to 14.5. The garage used a multimeter to check charging levels when stationery and came back at 12.68. Is this an issue with the alternator or is something more sinister occurring?
 

767wrench

Veteran Member
Joined
Jul 25, 2012
Location
Ohio
TDI
1981 Rabbit Pickup
Check your battery also. A bad battery may cause similar issues. Between the battery and alternator you should find the cause
 

Wathen316Uk

New member
Joined
Mar 21, 2016
Location
UK
TDI
VW Jetta 2006 1.9 TDI
Check your battery also. A bad battery may cause similar issues. Between the battery and alternator you should find the cause
Battery is apparently ok and holding correct charge. Just concerned that I'll change alternator and will be something else. Especially as it seems to charge fine when not accelerating.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
You may try it on another car just like yours. Lots of modern cars have "smart" charging systems that vary the alternator fielding for more efficient operation of the engine. So at light electrical consumer loads, the alternator output is scaled back.

In some cases the appropriate ECU will show this data via a scan tool. Target and actual voltage. If it is where it wants it to be, then all is good.

Nominal 12v battery is 12.6v. Anything over that, is "charging", even though the system is technically 14v. Many of the lights are controlled via varied voltages anyway, so it isn't like it will effect those. Again, all seen in scan data.

Since the engine needs most power when accelerating, it stands to reason you'd want the alternator to back off charging then, so there is less load. The air conditioner compressor will do the same thing.
 

thundershorts

Top Post Dawg
Joined
Jul 15, 2010
Location
west chester pa
TDI
2015 passat tdi sel premium 2015 golf s tdi gls tdi b5.5, 2002 eurovan,Peugeot 505 td,Citroen cx25 prestige
If battery is the original, its probably time to replace it before it fails and possibly causes alt damage
 

767wrench

Veteran Member
Joined
Jul 25, 2012
Location
Ohio
TDI
1981 Rabbit Pickup
Just for reference I have a scan gauge on my car that always displays voltage and its always 13.8 to 14.1 when running. 2012
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Just for reference I have a scan gauge on my car that always displays voltage and its always 13.8 to 14.1 when running. 2012

And your car is not the same as his, just FYI. Nobody in the US has the same car as the OP does.

VAG's "Bluemotion" trade name is a brand given to cars that have provisions in place to improve fuel efficiency. Things like, oh, I don't know, turning off the load of the alternator under certain conditions? :cool:

Again, I urge the OP to observe the same conditions on the SAME CAR, and see what if any differences there are. I bet there is nothing wrong with the car at all, and it is working as designed. :)
 

Locoelectrician

Veteran Member
Joined
Jan 10, 2015
Location
Ohio
TDI
2015 Passat TDI SEL, 2015 Golf SEL Sportwagen, 2005 Jetta TDI, John Deere 355D
And your car is not the same as his, just FYI. Nobody in the US has the same car as the OP does.
VAG's "Bluemotion" trade name is a brand given to cars that have provisions in place to improve fuel efficiency. Things like, oh, I don't know, turning off the load of the alternator under certain conditions? :cool:
Again, I urge the OP to observe the same conditions on the SAME CAR, and see what if any differences there are. I bet there is nothing wrong with the car at all, and it is working as designed. :)
This is what I believe, and I know for a fact BMW does this because they even have a gauge on the dash that shows it. Under normal driving they will only charge the battery to 80%, and the other 20% only happens during coasting.
 

VeeDubTDI

Wanderluster, Traveler, TDIClub Enthusiast
Joined
Jul 2, 2000
Location
Springfield, VA
TDI
‘18 Tesla Model 3D+, ‘14 Cadillac ELR, ‘13 Fiat 500e
I'll second oilhammer's suggesting. This car might be operating as designed... it's called alternator load-shedding.
 

tactdi

Veteran Member
Joined
Jun 21, 2010
Location
North Carolina
TDI
2005.5 Jetta
This is what I believe, and I know for a fact BMW does this because they even have a gauge on the dash that shows it. Under normal driving they will only charge the battery to 80%, and the other 20% only happens during coasting.
Due to BMWs search for fuel savings, cars are eating batteries, since they do not get fully charged. As you said, they get fully charged when coasting. But Americans do not coast, so the batteries are not getting a full charge.

http://www.roadandtrack.com/car-cul...710/enginerdy-strange-connections-bmw-n63-v8/
 

VeeDubTDI

Wanderluster, Traveler, TDIClub Enthusiast
Joined
Jul 2, 2000
Location
Springfield, VA
TDI
‘18 Tesla Model 3D+, ‘14 Cadillac ELR, ‘13 Fiat 500e

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
BMW has software updates for that, there are lots of TSBs floating around too. The other issue is, the AGM batteries that many (most?) of them now use is supposed to get a new battery registration in the car's onboard systems. If it doesn't, the charging system can not work properly and the battery life will be shortened. Really the same type of thing in a way that the hybrid cars have, although they employ a much more sophisticated setup for obvious reasons.

Interesting point about people not coasting, as I am sure we all see LOTS of that here. Morons speeding up to a red light, then slamming on the brakes. :rolleyes:

Useless trivia: when the dual-throttle-body-injection Civics came out in the late '80s, Honda started to use a charge toggle system to aid in smoother idle after a cold start, as well as lower fuel consumption and improved emissions during this normally richer running higher polluting period. Basically, so long as the electrical consumers were not overpowering the battery, the load sensor in the fuse block told the ECU to not field the alternator at idle, and this "grace period" if you want to call it that would last for a couple minutes some times. Which meant that a LOT of people were condemning alternators on these cars. Because they'd start the engine, then check the system, and see nominal battery voltage and think the alternator was not working. Put a new one on, same thing. But if you waited a few minutes.... boom, alternator gets fielded, voltage jumps up, everything working normally. :)
 
Last edited:
Top