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Discussion Starter · #1 ·
I took the family out for after turkey for shopping Thursday night, it was cold so headlights, bun warmers, rear defroster, front defroster so fan at max, I'm sure fog lights and radio too. Fan shuts off, lights go dim, battery light comes on. Rev the engine or drive above idle and the light goes out, everything seems normal. So I shut off most of the electrical toys and set the fan speed to manual and no problem but afraid to shut off the car. No prob as I don't believe in making people work on holidays so I waited in the car anyway.

Next day, check battery voltage after sitting overnight in about 30 degree F weather, 12.5V. Check when engine running and 14+V. For the next few days everything is normal.

Back to routine this morning, coasting down a hill, blower shuts off, battery light comes on.

I did determine if I have climate set to auto mode and auto fan speed, the battery light coming on causes the fan blower to shut off. I can manually run the fan when the light is on but I didn't keep it this way long enough to determine if the light would go off and on with the fan on manual but it doesn't seem likely that the climate control is causing this but anything is possible.

This follows my recent experience in the "Today was a bad day" thread
http://forums.swedespeed.com/showthread.php?183216-Today-was-a-bad-day
I have no idea if there is any relation to events listed there.

Any ideas what I should check?

The battery is a genuine Volvo batt, new in 2008.
 

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The B+ cables on these cars (especially 99s) are notorious for failing, sounds like yours are on the way out. Follow the cable from the battery to the main fusebox. Test voltage at the fusebox, and if you see a significant drop, I'd recommend replacing the cables.

Also, I'd check your battery terminals and ground locations for corrosion. I found a ground cable that was snapped clean off the ground on the front of the subframe on my old 98 V70 (surprisingly the car ran fine with it like that for an unknown amount of time!)
 

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Discussion Starter · #3 ·
Would I only expect to see a voltage drop on the B+ cable when the batt light is on or anytime?
That's the weird thing, how the light will just randomly go on and off. And when the batt light comes on, everything dims, almost like the alternator is just randomly deciding not to provide current or a cable is loose.

My next post may be, how to access the alternator and starter. I can't even see how to access the wires coming from the alternator :-(
 

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You'll see a drop anytime, but the worst should be when the light comes on as voltage has gone below the warning threshold. The drop should be more drastic the more current is running through your positive cable - ie the more electrical stuff you have on. Try to replicate replicate the scenario you had by turning everything on then check the voltage at the fusebox as andy suggested.

As for finding the wires coming from the alternator and going to the starter, they go to the positive post of the battery and you should be able to follow them from there.

Could your belt be slipping?
 

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Replace both cables
 

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Discussion Starter · #6 ·
Thanks for the tips everyone.

I'm just waiting for weather above 10ish degrees as I have to work outside and I hate snapping brittle plastic bits. If you don't know the joys of working in sub freezing, and even sub zero, everything plastic likes to go snap, copper wires are not very flexible and it is impossible to keeps hands warm when every tool or part you touch is freezing cold. I'll check if my garden is frozen enough to park my camper back there, I didn't do it before it got wet so had to wait. Oh yes, this matters to me because the camper is blocking my access to the garage.

Thanks again and I'll report back...
 

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You need to bring it to a HEATED shop or if you're doing this yourself, borrow a HEATED garage space.
You need to remove a lot of plastic parts to get the B+ cable installed and they need to be warmer.
If you don't do this I can guarantee some pieces will break as you're trying to do this outside.
I also suggest you get this done now or you may get stranded one night and that's not such a good idea with this cold winter we're all having!
 

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There is only one (1) B+ cable and one (1) positive cable
The B+ runs from the battery under literally everything (battery and tray come out) and winds up at the fuse box upper left side in the engine compartment

The other is called the positive cable.

Why they call the B cable, B+ is confusing I know. I guess it's because it goes to the positive end of the fuse box and runs from the positive battery terminal.
Both go bad so it's always a good idea to do both.

Which is worse right now? You need to test them
 

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Discussion Starter · #10 ·
I see I went and confused myself. I got ahold of a charging system wiring diagram for a 95-96 850 and noticed the generator is labeled B+ from the starter so I went around thinking B+ was battery to alternator. Sorry for the mixup. I'll get the correct wiring diagram and drop check voltage at the fuse block and try the test at the starter and alternator as well.
 

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Discussion Starter · #11 · (Edited)
It warmed up to about 40 degrees F today so this was my first opportunity to get out and do some basic testing.

I went for about a 10 mile drive, felt both ends of the B+ cable and it did NOT feel warm at all.

I removed, cleaned (emery cloth to all contact surfaces) and reinstalled the following:
Ground braided cable from the firewall to the engine
Batt negative to body between LF headlight and the battery
Both battery posts and cable ends that connect to the posts
Battery end of the B+ cable

I also visually inspected the other batt neg cable that goes to the bottom of the engine block and it appears to be perfect. I did not directly test this connection but I'll confirm below, good connection to the engine block.

Next, I checked battery voltage and compared to several other points in the engine bay. This was done after the short drive and with the engine off. The reading is not important but the differencees between the readings and the battery voltage. Most are less than a hundreth of a volt off so I am somewhat releived that my cabling is at least decent. I do understand that I should go ahead and do the B+ cable no matter what I find but I had some time so I started testing.

Battery - post to + post = 12.83V (resistance is .7 ohm)
Battery - post to + post inside the fuse box (the other end of the B+ cable) = 12.83V
Battery - post to + post on the alternator (tests positive battery cable from the batt, through the starter to the alternator) = 12.83V
Battery + post to ground bolt on firewall = 12.83V
Battery + post to ground bolt on L strut tower = 12.83V
Battery + post to batt negative cable where it connects to body between LF headlight and the battery (resistance is 1.1 ohms)
Battery + post to engine block = 12.83V (no, the meter is not stuck or on a data hold mode)
Battery + post to body of alternator = 12.83V
Battery + post to subframe = 12.72V Is the subframe supposed to have its own ground? I didn't see one, maybe I need to check this.

Next, I'll do some checking with the engine running around 2000 RPM and a bunch of accessories turned on. My helper wasn't feeling well today so that has to wait. I put a 10A charger on my battery for a few hours a couple of days ago. I have not seen the batt / generator light for a few days so I'll be cautiously optimmistic and do more testing when I can. I'll also plan on doing the B+ cable anyway. To be continued...
 
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