Alternator Workshop

[PeteK]

This warning flashed up on my 2004 Passat 130TDi on the drive home from work last night; the alternator light came on for a second or so and then went off after which the message disappeared. I drove home with no further issues and have done another 20 miles today again with no problems. It was raining at the time it happened, although I don't recall going through any deep puddles - I had also switched the aircon on a few seconds before. I have checked with Vag Com this morning and cannot find any faults stored (i'm not sure that the alternator would generate any DTC's anyway?) and the alternator belt appears correctly tensioned. Is it possible to measure the alternator output voltage from Vag Com?

I wouldn't normally be too concerned over this, however i'm due to take the car to France in 4 weeks and will be covering 2000miles or so! Any advice would be appreciated - can this be caused by a momentarily slipping alternator belt due to the damp weather or do you think my alternator is about to expire?

Thanks for any advice given,

Pete

[DSG4ME]

Thats normally one of two things, if you are lucky the battery simply wants charging, if you are almost lucky then you want a new battery, and if you are SOOL the alternator is on it's way out, worth getting tested as the clutch pulley does go and can be replaced for less than a whole new unit.

[martin1810]

Extra load from air con pump probably made belt slip for a moment and flash up light. I would ignore it. Stick a multimeter across the battery terminals . As long as voltage rises over 14v with a few revs you are good to go.

[PeteK]

Thanks for the replies; i've just spoken to my mechanic and he also advised me that it was probably just a momentary belt slip which has caused it. He had the same thing occur on his Golf and it has never happened again since. I've done about 100 miles now with no further issues - the battery is charging fine and the tensioner is also ok. Fingers crossed it won't happen again, however i'll report back if it does!

[boidy]

i don't want to worry you, but the same thing happened to me.
the warning came on the dash but it was 6 months later that my auxiliary belt tensioner and the alternator clutch pulley went. these are common faults on passats.

just check that the auxiliary belt doesn't appear to lift off the rollers when the engine is idling. if it does you'll hear a chattering sound from under the bonnet

[PeteK]

Thanks Boidy, i've checked the belt and tensioner whilst someone was revving the car. Both appear fine - there is only minimal movement on the belt tensioner when you rev up. My mechanic advised that if it was on the way out, it would be bouncing all over the place. I've now done a further 100 miles since yesterday and no further problems have occurred.

[DSG4ME]

Slacken the aux belt and pop the belt off, then spin the alternator pulley with your hand, if it rotates freely both ways the clutch pulley is on it's way out, if you can feel a winding down resistance this shows it's still pretty good.

[casman]

I have a similar problem on my Mk4 2003 Golf 1.9tdi. While on the motorway the 'Alternator Workshop' warning light comes on intermittently. Sometimes at 60mph, sometimes 70mph.

I had the alternator pulley replaced about 15k mls ago. Anybody got any ideas? Could it be a belt problem?

[stonedagain]

Slacken the aux belt and pop the belt off, then spin the alternator pulley with your hand, if it rotates freely both ways the clutch pulley is on it's way out, if you can feel a winding down resistance this shows it's still pretty good.

Easier way: Poke a finger through one of the holes at the front of the alternator & try to turn the armature. If it will turn one way but not the other, the clutch is ok. If it won't turn in any direction, it's siezed. For obvious reasons, don't try this with the engine running!

[PeteK]

Just a quick update to this, also covered in this thread https://www.vwaudiforum.co.uk/forum/s...154#post554154

Boidy, your advice was very accurate! Unfortunately on the way to the South of France, the alternator pulley did fail causing a loud noise at idle. However I was able to complete the journey with no issues.