Can vagcom test battery/alternator?

parking_question_chap wrote: »

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.

I wouldn't go to kwik fit for this type of thing. It should be straight forward but the only thing i'd go to kwik fit for would be tyre change and A/C.

I know the knee jerk is to say Kwik Fit can't do even those things but i've known of supposedly good garages doing them badly too, well the tyre fitting at least.

parking_question_chap wrote: »

You average kwik fitter will have been trained to be able to fix certain things. However, where they have a problem that does not follow the set script they have laid out for them, they often dont have the experience to then logically work out what the problem is based on the information they are presented with.

Yes you might find one of their branches with an employee who has been there years and knows cars inside out, which is great, but from my experience watching in the car park, its usually just young chaps. Plus at the end of the day, problem fixed or not, they are still getting paid by their employer. If you go to the local indi and they dont fix the problem, they will not get paid until they do.

Im just telling you my experience of electrical issues. But pays your money takes your chance and all that.

It's a very true point you make. I see it in my workplace and i'll admit that i'm one of them. If a customer comes in getting all upset over whatever or if a manager starts getting upset for whatever reason, maybe some equipment breaks which sets us back .... well i'm still getting paid. I can understand the boss getting all mad because his profits are down but when those on the peasant line like myself start getting upset i can't relate or understand. Why you getting mad? We're still getting paid. Not to say that i only put in the bare minimum effort because that isn't true either but you get what i mean & i see your point.


The only thing is i don't know anywhere local doing A/C. As said the garage i've used in the past is 30 miles away and my next holiday isn't until the end of August.

But back on topic i just ran VCDS and the readout fluctuates between 12.40V & 12.50V.

JustAnotherSaver wrote: »

But back on topic i just ran VCDS and the readout fluctuates between 12.40V & 12.50V.

Ok an update on the above.

In my quote there that was when the battery charger was still connected and the car was not running. The charger had been connected since about 5:30pm yesterday.
I've a feeling the response will be "well of course that'll be the output" but then i'm an electrical dummy so i don't know.

We took the car in to town which is a short drive, parked up, came home, i took it through to my mothers which is a little longer but still a short drive at maybe 4-5 miles.
Did an oil and all filters change on it as it was due.
Stopped off at the garage on the way home to put some juice in & when starting it up from the garage to the house it didn't chug-chug-chug on startup but it didn't start as cleanly as usual either.

I brought it home and plugged in VCDS again out of curiosity - this time the engine was running.

The readout this time fluctuated between 10.70V-10.80V.

I did a bit of googling while it was connected as i wondered how i could use VCDS to test the A/C out of curiosity. This only took a couple of minutes. I couldn't find anything.

After those couple of minutes i went back to the test which was now fluctuating between 10.50V-10.60V.

We'll see if it starts in the morning.

These are just numbers to me but does any of this mean anything to you knowledgable folk?

khcomp wrote: »

If the battery voltage is 10.7v with the engine running, you have a definite problem, possibly a faulty alternator or a terminally ill battery. Not much help there, as you will need to remove the battery and test that on it's own. You also say that you measured the battery voltage whilst charging - this will give you the voltage output of the charger, which tells you nothing.
As you can see from Adrian's table, there's only about one volt difference between a good & a faulty battery - somewhere 'between 11v and 15v' isn't anywhere near accurate enough.
Please, please go back to my original posts and check the battery whilst it's off the car after being fully charged & then left for several hours. Your diagnostic software may be more fun to use, but it is not helping you in this case.

No problem. I just wondered if it could do the job that's all. If it could & if it could be done with the battery on the car then it'd just be easier than having to faff around taking it off.


Oh i've just had a thought - can you (a garage) test if a battery is good or not without it being disconnected? Or even the alternator?

If so then i could just see the manager at the HGV garage on site at my work. I'd just have to take my wifes car to work tomorrow as if there's such a tool to test while it's still connected then they'll have it.

But if it needs to actually come off regardless then i guess there'd be no point in that exercise.

m_c wrote: »

Battery sounds fine, but the alternator isn't doing anything.


Voltage should be well above 13V with the engine running. If the battery was preventing the alternator from getting above 11V, then you'd have far more noticeable problems.

Is there a way to test if the alternator is duff?