Volvo V40 charging issues

Alternator earth and ignition feed to the alternator are probably worth checking 1st. Followed by the possibility you've got a 2nd duff alternator.

Are you certain the battery is ok? Be worth having it checked.

I'd also measure for voltage drop in the circuits.

Connect the DVM from alternator output to battery positive and check the voltage with the engine running. Should be less than 0.2v. Do the same between alternator body and battery ground terminal.

With a good battery fully charged and no load other than the engine electrics you should see 13.8 volts.

the battery should show 12.8 or very close to it when fully charged, check out the battery first. Then wiring, then get the alternator tested off the car.

IIRC there was a one way clutch that can fail on the alternator of some volvos, which might mean the alternator is not getting enough of a spin.

On 16/02/2012 19:39, Mrcheerful wrote: .

Do modern alternators all have regulators built in or is there any possibility of it being external?

AFAIK they are all built in now, the last external one I saw was on something old and japanese, a truck or 4x4. Do you have a working alternator charge light? if that fails it won't charge.

I asked as I once had a car that wouldn't charge and it was eventually traced to the wire from the 'F' connector on the alternator shorting to deck in the loom. Obviously this wouldn't apply to one with a built in regulator.

Alternator earth is the same as the engine earth, which is fine. I've tried running a jump lead between the engine and battery negative - no change. Ignition feed (from dash light I assume you mean?) not checked yet - so worth a go, thanks.

I think so - a battery failed in a year or so and was replaced under warranty - with a warning if it happens again in a similar time that the car is likely to be the cause. (And it probably is!)

Will test at the weekend... > With a good battery fully charged and no load other than the engine

I don't think I've ever seen that high on this car.

I've had the one-way clutch fail in my other car (Diesel V70) - it seized meaning no one-way action. Result noisy drumming sound from drive-belt at idle speed. I don't think the V40 has one, but will check.

I'll re-check battery voltage after charging. The dash charge-light works as expected, but I guess it could be resistive causing strange results. Will check further.

It's the same on more or less any car.

Have the Volvo a fuseable link in the wiring harness charging circuit somewhere near the battery - this maybe have dirty/corrosion connections.

It's worthing checking it's actually earthed to the engine though, sommetimes you can find enough corrosion in the bushings to give you a small volt drop.

I agree it should be. I didn't have a reason to look at the charge voltage on this car until this fault occurred - so while it should be at least 13.8v I've never seen it that high. Hopefully I will again soon!

That's why it's worth doing a voltage drop check as I described. Saves any guessing.

autodata shows three different alternator setups with different wiring for each, so if you count the wires and get the colours it may help. One has one fuse, one two and one three, including a 120 amp fuse on the output! One has an additional module that is shown as separate. etc.

In message , "Dave Plowman (News)" writes

Only with the engine running, & alternator charging, surely?

I had a car with some strange charging habits. After three alternators I eventually worked out it was some tracking across the wiring loom plug which went into the alternator. It was really hard to see, but a new plug fixed the issue.

Mr C: Would the VIN number help confirm which system this car has? I'm not with the car today so can't check wires until tonight, but it would be useful to know how the system *should* work. (I can get the VIN from the paperwork, which I do have now!)

it might help at a main dealer, but Autodata does not have that facility, sorry.