Can vagcom test battery/alternator?

JustAnotherSaver

I'm wondering if either is on the way out on my wifes MK4 Golf (X-plate).
I don't really want to go to a garage tomorrow (Kwik Fit being the only one open locally) and say hi can you test this for no charge >IF< vagcom can do the job for free. I have a full version of vagcom, i'm just not great at using it fully.



Car had been ok for long enough. Battery is maybe 12-18 months old. A tyre was flat yesterday so i had the car running while using the compressor to blow it up.
Wife drove about 20 mile out. Didn't start great but started. When she came to come back home the car wouldn't start.
I jumped it and as she approached home it started to judder a bit i think she said. Then she parked it up on the drive. Came to start it again and it wouldn't start.

All dash lights come on as they should. Fans blow as they should. Radio will work. Remote locking still works.

I've got a battery charger on there at the moment but having a chat with someone about it they say it'll likely be the alternator.

Just wondered if there was some reading or test in vagcom that would help identify if either battery or alternator is good.

AdrianC

All you need is a multimeter, or a simple voltmeter of some kind. What voltage are you seeing across the battery terminals with the engine off, idling, and at about 2,000rpm?

It should be about 12.5v engine off with a charged battery, probably north of 13v idling, and around 14.5v with some revs on.

I'd be surprised if the diagnostic software can't tell you that.

khcomp

VAG-COM will show you live voltages, but as said above, a multimeter will do the job fine.
Charge the battery fully, leave it disconnected for 12 hours and then check the battery voltage. Anything under 12.5 volts, and it' pretty certain that your battery has had it. If that's OK, reconnect it and start the car. Let it tick over and measure the battery voltage again. It should read about 13-14 volts ( ideally around 13.75 volts plus). Check again with headlights, blower and wipers on full. Anything below 13 volts, and your alternator is probably no good unless there's a wiring fault.

Sam_Fallow

If you are just using it for shorter trips and have a lot of accessories on all the time then you may just need a good 24H charging session. A jump start and a 20 minute drive won't do it.

A failing alternator will usually put on one of your dashboard lights.

Geoff1963

Wife drove about 20 mile out. Didn't start great but started. When she came to come back home the car wouldn't start. I jumped it and as she approached home it started to judder a bit i think she said. Then she parked it up on the drive. Came to start it again and it wouldn't start.

The battery is needed to start the engine, and also to support the engine running loads for about 1/2 hour if the alternator fails. That sounds about what you have.

The charge warning light goes out as soon as the alternator is doing "something", so it is on if the engine is stopped / drive-belt broken etc. It may be off if the alternator has just lost one coil or one diode. One sign might be interference on the radio, as the alternator half-works.

JustAnotherSaver

AdrianC wrote: »

All you need is a multimeter,.

These things sound like a wonderful piece of kit. The only thing is i wouldn't know how to use one. There is one at my mothers i think but i wouldn't know how to use it.
However if someone was able to say click this click that after loading vagcom up then i could easily read off a readout.

m_c

If you select the engine module in VCDS (It's not been called VAG-COM for a good few years now), then Advanced Measuring Blocks, search the list for something like Battery Voltage, Supply Voltage, Terminal 15 or 31 voltage - I'm not sure what name they'll use, but if in doubt just try anything with Voltage in the name.
Tick the box next to it, and it should show the value in the main window. If the value is somewhere between 11-15V, then it should be the battery/supply voltage.

khcomp

JustAnotherSaver wrote: »

These things sound like a wonderful piece of kit. The only thing is i wouldn't know how to use one. There is one at my mothers i think but i wouldn't know how to use it.
However if someone was able to say click this click that after loading vagcom up then i could easily read off a readout.

Just set it to the 20volt DC scale (a solid line above three dots, not the wavy line) and follow my instructions: There will be 2 wires with probes on the meter - the red one goes to the battery positive terminal, the black to the battery negative.
VAG-COM can't test the battery when it's off the car, so may not be of much use for the initial tests.

JustAnotherSaver

Thanks.
The battery is still connected. I was going to d/c it but decided to just leave the charger under the bonnet connected up as it's easier. We're on a pretty quiet street in a not bad area so

So if it's between 11-15V then it's bad? I thought the battery was a 12V supply so if it reads as 12V then isn't that good?

AdrianC

Nominal 12v.

parking_question_chap

From mine and friends experience MK4 golfs are prone to electrical gremlins. Indeed if there is a car on the horizon with one of the lights not working its usually a MK4 golf.

Find a good indi car electronics specialist, they are worth their weight in gold. Whilst you could get a multimeter, ask yourself if you really know what you are doing.

Personally I wouldnt go to Kwik fit either. You want a bloke who has years experience in the profession.