low voltage output until engine is revved

[archiboy24]

Has anyone else experineced this? When the car is started, the voltage gauge shows less than 12v and my battery light and ABS light stay on. If I give the engine a little rev, everything goes to normal. It doesn't sound serious, but it is a little annoying! Anyone know the cause and/or fix?

[Vagsport]

I'd say the voltage regulator at the back of the alternator.

Siena

[newsh]

Or the belt is loose?

[nostrixoxide]

At what RPM does your engine idle at? I only ask because if it's not the voltage regulator or a loose belt then possibly your idle is too low. Just a thought, good luck with the repair...

[SteveH]

I have the same happen on my S2. Belt is new and the idle is above 800 rpm. Must be a wiring fault or the regulator

[S2 Ant]

Usually the alternator wont start to charge correctly until something like 1400rpm or there abouts, on new alternator's ive had in the past it says on the spec where it starts to charge from...

Possibly the regulator as said above as these wear out.

[Craig]

Lights

Hi

I have the same problem. As soon as you give a little revs, the lights go out and the cars fine. I had a diagnostic check done recently and there is an error on something called the idle switch. Anybody know more about this.

Cheers
Craig

[S2 Ant]

Thats possibly the switch i mentioned, alternators are designed to not start to charge until revs have gone past a set limit first.

I guess its that?

[Jamo]

Usually the alternator wont start to charge correctly until something like 1400rpm or there abouts, on new alternator's ive had in the past it says on the spec where it starts to charge from...

Possibly the regulator as said above as these wear out.

I've never heard of this, it would be possible to flatten a car battery on idle if this was true, just doesn't seem right. Think it might point to the revolutions of the alternator and not engine revs.

[archiboy24]

Well I replaced the entire alt. with a known working one yasterday, but I get the same result. Could it be from a weak battery perhaps? I know my battery isn't fully charged as I've been doing a lot of starts while testing the engine.

[SteveH]

Mines been doing it for over 2 years and the battery is Ok. I can only think it's a voltage threshold in the autocheck, electrical system or alternator regulator that isn't being triggered until the alternator puts out more than a given number of volts. 9 times out of 10 my lights stay on until the throttle is opened slightly, then the lights go out and stay out until the next time I start her....strange but harmless

[Alistair C]

Sorry to re-open an old thread here..... but needs must!

I've had this problem for a while now - and finally had the regulator changed for a new one today.
Unfortunately, this new one wouldn't allow charging to commence at all..... leading to a dead S2 at junction 13 on the M25!

The AA man came and put the old reg back on and this got me back to Square 1 - but at least it now was charging!

What did emerge from this very thorough AA man - was that the circuit which primes the magnetic field (the blue wire on the alt?) was not doing its job. Where the Alt light should light up then go off as soon as the engine is starting - mine just isn't lighting at all. Apparently, the alternator will self energise and start charging once the rpms get high enough, but it isn't an ideal solution.

I've checked the dash cluster bulb and it seems in GWO. So the quesation is - what might stop this circuit functioning? Is there a fuse somewhere I don't know about?

Unfortunately this failure sequence isn't in the handbook!

[quattronutter]

maybe a fault with the instrument cluster itself?,check to see if you have a live at the main plug going into the cluster,if you have no battery light the alternator wont charge until about 3k rpm,best get an electrician in to check continuity of the wiring,its probably a dodgy wire somewhere in the under dash spaghetti maze...

[SteveH]

Sounds like a question for the sparkies on the Forum. I know I've heard the blue wire mentioned before and it does have one or more important functions..My lights are still remaining illuminated on startup and the volts read low until the engine revs are increased. I'd like to know what to look for too

[WabTheKing]

cheap voltage regulator, mine started doing it when i put a german and swedish one on, basicly you get what you pay for!!!!!