02 Polo 1.4 Auto - power steering light, then charge light

[Midge]

Was going down the motorway this morning when I got the power steering warning light come on then a couple of minutes later, the charge warning light.

I wrestled it back home without the power steering - about 7 miles - and then pulled the bonnet expecting to find the aux drive belt missing (assumed because both came on within a few mins of each other that it might be a crank driven steering pump), but all was well - all tensioned correctly etc.

I've since established its an electric power steering pump anyway!

On restarting it, there there was just the charge light which remained on - i.e. power steering pump light had gone out and power steering was back in action. I've since restarted it several times and the power steering continues working OK, and charge light continues to glow.

The battery doesn't seem to showing any signs of weakening yet in spite of several starts which made me wonder if it was actually being charged so stuck a meter across the battery with engine running and its about 11.7V dropping to 11.1V when the fan, air con, lights etc are on. Lower than the 13-14V it should be for sure so doesn't seem to be being charged.

Any ideas? It's only done about 43K so I can't imagine its alternator wear. Regulator maybe?

I've had my fault scanner on - and the only thing I found was in the ABS system which was:

00668 Battery Power Voltage Supply (Terminal 30)

I cleared that error expecting it to come back when I next started the car, but even that has disappeared now and might not have been anything to do with this issue.

Engine code is BBY.

TIA Midge.

[Midge]

OK - just a bit more info. I've dug out the alternator and bench tested it by sticking it across a spare battery, with a 2W lamp between B+ and the L (lamp) terminal and spun it with a drill. Lamp stays lit and no sign of a charge voltage so same symptoms as in car.

Brushes and slip rings are relatively unworn, and rotor resistance is fine.

What I'm struggling with is understanding how I can test the windings and diodes and therefore prove whether its the alternator or regulator. Anyone got any diagrams/guide for the Bosch alternator?

Midge

[Crasher]

Check the strip fuses on top of the battery, not just visually-undo the M6 nuts and remove them as they crack very subtly and look OK until removed.

[Midge]

Thanks for the reply crasher - but as per my last post, I've actually tested it outside the car using a spare battery and my jump leads (+ a test light) and I seem to get the same symptoms.

I'm pretty sure after I dug it out that I did a continuity test from the common side of the battery fuses to the end of the cable too - which would have proved the strip fuse, but I will double check it to make sure.

Midge.

[Midge]

Well I've found some general diagrams on how an alternator works but they don't help me a great deal as the stator windings and diodes on this Bosch are all crimped up and it looks like it would be a destructive process to pull it all apart.

So the only conclusion I've been able to reach is that its unlikely the windings themselves have gone, so that leaves the six diodes. I've a diode tester on my meter so took three rectifier diodes I had knocking around and measured the volt drop across one (0.51V) then two in parallel (0.48V) and then all three in parallel (0.463V)

I got exactly the same reading between the B terminal and the ends of the diodes I could get to on the alternator (shown as 1/2/3 in diag below), and again, 0.463V between the frame and the diodes. The measurement from GND to B terminal was double this as I'd expect - around 0.9V.



|-----------|<|--------1----------|<|-------|
|-----------|<|--------2----------|<|-------| Frame/GND
|-----------|<|--------3----------|<|-------|
B

The stator windings connect in at 1/2/3 too so would expect low resistance between them.

So it kinda looks like the alternator is OK and its going to be the regulator. Any views on whether my logic stands up?

TIA.

Midge.

[Crasher]

I wish I had that amount of time to diagnose a faulty alternator but if I did what you have done I would be charging them £500 to diagnose it as faulty before fitting a new one anyway! If the alternator does not kick out at least 13.8 volts on my DMM then I fit an exchange unit.

[Midge]

Lol - fair point crasher, and if I was making a living from this, I'd do the same!