I am going to throw this out here to see if anyone has seen this problem before. According to a voltmeter I have mounted on my dash board, sometimes the charging voltage will drop as low as 11.9v, even while driving down the highway at 70 mph. Dealership cannot find anything wrong but replaced the voltage regulator anyway. Please read the following entry from my log and see what you think.

1/13/2017 – Drove XC70 to friend’s house to check on it and to Valero station to top off the fuel tank before leaving for Schertz hamfest. Charge voltage seemed fine and was holding at 14v, whether I was moving or stopped. Temperature was 72 deg. A few hours later I left the house for San Antonio. The charge voltmeter was pretty steady at 13.7-13.8v and remained that way until reaching the center for the event in the San Antonio area. Later that evening when I left the center the voltmeter was reading 13.1v. The same problem was occurring, when I let off the accelerator pedal the charge voltage would shoot up to 13.8v and when I pressed on the accelerator the charge voltage would fall back down to 13.0-13.1 volts.

1/14/2017 – the next morning I left the hotel I was staying at and proceeded to the event I was attending. The charge voltmeter was reading 13.0-13.1 volts, the same as the night before, and had the same response to whether I was driving or coasting. Later in the day around 2:00 pm I started my 3 plus hour drive back home from the San Antonio area. The charge volt meter was reading 13.0-13.1v but after 10 mins of driving it slowly climbed up to 13.7-13.8v and was stable, whether I was driving, coasting or stopped. Then at 3:00 pm, after an hour of driving on the freeway at 70 mph, the charge voltage dropped back down to 13.1v. And again, the voltage would shoot up to 13.8v when I let off the accelerator pedal and started to coast. Around 3:30 pm, still cruising at 70 mph, the charge voltage dropped to 12.4-12.5v. Now I started to sweat as the system was not even charging the battery and I still had almost 2 hrs until I arrived home. Again, the voltage would shoot up if I coasted and dropped back down when I pressed on the accelerator again. A few minutes later the charge voltage dropped to 12.1-12.2v. And again, the voltage would shoot up to 13.8v when coasting. While I won’t really say it was “stable” but if I turned on the lights and high beams, the voltage would not drop any farther.

Now here is where it gets interesting………

I started to pay attention to some other things and here is what I see going on. At the time, the charge voltage difference between driving and coasting was very repeatable every time. Even the times I used the cruise control, when coasting down a hill, such as an over pass, the voltage would shoot up to 13.8 volts but fall to as low as 12.0v when the accelerator was reapplied. Now, when I came to a stop such as an intersection, the charge voltage would drop to the 12.0- 12.4v range. While coasting to a stop I noticed that the charge voltage would stay steady at 13.8v until the engine would drop below 1500 rpm and the transmission would shift into first gear, then the voltage would drop to the 12.0-12.4v range. This was very repeatable once I got off the freeway. The very interesting thing is that the engine rpm alone does not affect the charge voltage. I can be stopped with the transmission in park and rev the engine up to 2000 rpm with no change or increase in charge voltage. I tried the same thing with the car in drive, with one foot on the brake and the other foot holding the accelerator pedal so the engine was at about 1700 rpm. There was no increase in charge voltage. The car had to be moving and coasting for the charge voltage to climb to 13.8v. I am starting to think this is not a voltage regulator or alternator issue but a PCM or ECU problem as it involves the transmission and the vehicle in motion.

The next day after my XC70 sat overnight, the charge voltage was fine and holding steady at 14.2-14.4v while idling in Park.

I just wanted to see if anyone has seen this before. The dealership seems to think this is normal, but I do not buy it.

Dan

 

Have you had any warning messages? Specifically, the "Power System Service Required" message with the red battery light?

 

No, I have not had any warning messages. The car seems to go through batteries though. The battery had to be replaced when I bought it used in Jan 2015. I had to replace it again in Nov 2016 after only 22 months when I stared getting the "Low Battery" message. The dealership I have taken my XC70 to has not been able to give me any information on how the Volvo battery charging system works. When the charging system acts up like I described, it has happened twice that I know of. I did not start monitoring the battery voltage until this last Summer when I installed a ScanGauge so I could monitor the water temperature. I then noticed that the battery voltage was running lower because of it being hotter outside which I can understand. I don't understand why the voltage can fall so low when going down the highway and climb back up when coasting.

 

When did you get the "low battery" message? When the car was running? Or when sitting with the key on engine off?

 

I wonder if somebody dreamed that up as a fuel economy enhancement thing.


P.S. Did a little searching. Turns out somebody did dream that up. Delco's keyword for that is "regulated voltage control". I don't see a way myself to determine what your car is supposed to do, and what it's not. I had not heard of this before. There's not much meaningful discussion of it on the web.


Fooling these systems does seem to be a subject of some interest on the internet.
https://www.motor.com/magazine-summa...arging-system/#

 

It's more than likely normal. The ECM regulates the output of the alternator. If there was an issue, the car will let you know. I'm sure the dealer did an alternator test. Frankly, I'm surprised they put a voltage regulator on it.

 

Thank you for all the replies. The car started displaying the "low battery message" while it was off. That's what prompted me to replace it as the same message was displayed when I purchased it. Then, the message would appear as soon as I turned the car off.

The dealership tested the alternator and their equipment told them it was fine, but they replaced the regulator in case it was intermittent.

If you read the post I made, don't you find it odd that the voltage would drop so low at 70 mph going down the highway and when I coasted the voltage would climb to normal? It doesn't make sense to me. The car behaved that way for 2 hrs until I arrived back home. Then after sitting for 24 hrs, I started the car up and at idle the voltage was fine at 14.2-14.4v. I can tell you it is not a comfortable feeling when you are over 120 miles from home and your battery voltage is less than 12.5v. I am still trying to get the dealership or Volvo itself to send me some information on how the charging system works.

 

I don't find it odd. While you're going 70 and have been driving some time, the battery is charged. So there is no need for much or any charging.

After the car sits and then is started, it needs some charging so charging voltage is back to 14v.

The CEM monitors calculates battery temperature. The CEM also monitors electric load and determines how much is needed. It communicates with the ECM which then varies the charge voltage.

If there was a problem, the car would tell you.

 

Oh, and thank you "firebirdparts" for the link to that article describing how the newer charging systems work. Explained a lot and just goes to show you that somethings are just over engineered to the point of being ridiculous. I have one question. If my 2012 Volvo XC70 has a battery temperature sensor, where is it located? I can see that if the sensor is intermittent and telling the computer the battery is too hot, it will cut off the charging.

Ok ES6T, explain this then. Back in mid December, this very same thing happened when I tried to start out on a 5 hr trip and the car had been sitting for 24 hrs. From the time I started the car, the battery voltage stayed at 12.0v until the car was in motion & coasting. Then the voltage would jump to 14.2v, kind of like what the article describes can happen. I got 5 miles from home, turned around and went back home to change cars. The XC70 sat for 2 days until that following Monday morning when I drove it to the dealership to get it looked at. During that 50 min drive, the battery voltage stayed constant at 14.4v and never changed while in motion, coasting or stopped. When I picked up my XC70 5 days later, it was back to doing the very thing I was taking it to the dealership for. I showed it to the Service Director and he could not explain it other than their equipment said the alternator was fine. I few days later the charging problem cleared up until mid January when it all happened again.

 

There is no battery temperature sensor. It is a calculated value, not measured. The alternator test the dealership does measures the charge while simulating different temperatures.

Sorry, but I do not think your car has a problem. I do not know the logic the system uses to determine when to charge and how much. Volvo does not give us that information.

 

The only way I could make sense of that would be to conclude that it had a mode to charge only when coasting, and it entered that mode. To me, it sounded suspiciously like something that somebody did on purpose. If so, then it also sounded suspiciously like something that would happen on the freeway after prolonged operation. That would be the perfect time to shut the alternator completely off, I get that. I bet the alternator was indeed totally off when it dropped to 12.4.

Now, I admit, I was unaware that cars had charging "programs", but when I started poking around on the web, some sources said PCM or ECM-controlled charging spread into most cars shortly after Y2K

I will also admit that I have no idea how the car is supposed to behave.

 

Well, there may not be anything wrong with my XC70 but it is unsettling that the voltage would drop that low. I could understand if it cut back to around 13v after peaking the battery but not 12.5 or less. That can be damaging to the battery, which could explain why the last Volvo battery did not last 2 yrs. I guess that could explain why my XC70 does not have a volt meter because they do not want you to see what is going on. I have noticed that on my Wife's 2014 Buick Enclave that the voltage will drop to around 13v but only for a short while and then climb back up to around 14v. Maybe it is a bug in the Volvo XC70 software because the last couple of times this drop in voltage has happened, it would not clear until the car was turned off for sometimes 12 hrs or more.

Anyway, thank you ES6T and firebirdparts for the advice and more importantly the article that explains the newer charging schemes.

 

Hi. I had the issue when "battery low" pops up on a battery that was replaced by dealership last year. Found the cause of problem. They did not reset the BMS. I fixed it by myself. Contact me if you still have problem with your battery and I will try to help you.
Alex

 

Hi Alex,

Any information you have I would appreciate hearing about. Do you have an email address I can reply to directly?

Dan

 

HOLY SMOKES !!!
This is EXACTLY what my 2016 XC60 T6 3.0 started doing last week !!!!!

It's 100% repeatable in acceleration vs deceleration voltage jumping.

 

I'm wondering if the Shunt used to provide this system data starts doing this erratic behavior if it's going bad.. ??

My 2016 literally started doing this totally out of the blue after always having a steady normal running charge voltage.

I replaced the alternator and it doing the Exact same thing still.

Going to check prices on the shunt module tomorrow at Volvo