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Alternator / battery failure warning -how to test alt / reg?

CarreraMonkey

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2 Sep 2013
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2,188
So the alternator / battery warning flashed in yesterday, but went off shortly afterwards. Today it came on permanently. :roll:

My indie can't do anything for at least 2 weeks and I need to get the car back on the road before then as it's my daily. Having read the procedure, it seems relatively easy to replace and within my abilities and tool set.

However, before I invest in a replacement alternator, I think I need to test to understand if it is the regulator or alternator that's failed.

I'll check the current across the battery terminals to see what the voltage is and I expect it will be less than 14v with the engine running.

My question is: Is there anyway to identify if the issue is with the regulator or the alternator? What do I do / how do I do it?

Many thanks!

Matt
 
Initial test shows 12.4v across the battery with the engine turned off and 13.3v with the engine running. Tried at tick-over and 2000rpms and no difference in voltage.

Interestingly, the warning light has gone off again. Suggesting that the voltage must drop as the temperature increases up to running temp?

I don't know if alternators are usually affected by heat when they're buggered, or if it could be the lead that's had it. Certainly, it's always had hot starting issues and I always intended to replace the starter motor lead. Could it be linked? :?
 
To test the alternator you have the car at idle , meter on the battery and a full load .. everything electrical turned on that you can.

Rule of thumb and anything above 13 volts and its all working fine .

I would like to see 13.2 on a 997 though.

Less than 13 volts and you have a lead or an alternator fault , you would check it at the alternator to prove a lead fault .. it will be higher and if 0.6 of a volt then you have proved you have a lead problem.

Ok so testing at the alternator isnt easy , you have to pierce the cable with a sharp probe on your meter and your pretty close to the moveing bits !

So again rule of thumb .. if you have a lead fault you will also have a slow starter motor .. so if it starts ok (spins nice and fast ) then we can , without checking , almost rule that out .

A lead fault will be permanent .. it cant come and go .

I only replace the alternator so have no experience on the regulator im afraid .


Now to throw a spanner in the works ...

ONLY on a C4 and i have ONLY seen this once since 2004 .. i had a car that did as yours is doing ..

Intermitent warning message then ok ..

The car had a clutch fitted a few monthes before hand , the main power lead to the starter / alternator exits the inside of the car to the outside at the back of the gearbox and then is bolted to a connection point further along .

At the gearbox rear bracket its held in place by a plastic clip on that bracket .. they hadnt fitted it so the lead was loose.

On a C4 you have a propshaft , the dam cable had rubbed through on the rubber doughnut , that in its self was ok but the x4 bolts also touched as it rotated causeing a direct short ..

Could have been nasty had the car stoped with the bolts touching the cable but in the end the symptoms were as you describe , i only found it by checking the gearbox connection and seeing what had happened ..

You can just about see it when peering through the under trays .

So .. imho its most likely an electrical fault in the alternator but as you have a C4 then its worth just haveing a look at the cable at the back of the gearbox .. O/S/R .
 
Thanks Demort!
So I switched everything on, interior lights, headlights, fogs, hazards, fans, pcm etc.

multimeter reads 13.18 - 13.2 (switching between the two as the hazards were blinking on and off) - which kind of suggests that the alternator is putting out what you'd expect (perhaps a little lower)?

Next stage is to test at the alternator, although I Have to confess not knowing which wire I need to test and where I need to pierce the casing! I'll have a look online to see if I can find some guides, but any advice or pictures would be helpful.
 
The cable is about 1 cm wide .. its black , it has a short rubber section close to the alternator body then its a corigated cover.

You have to get the probe in the rubber bit .

Its not easy to test and sometimes not possible .. its not designed to be accessable this way but its the only way to prove a high resistance lead .. which to be honest i dont think you have .

BE Carefull !

My opinion is an alternator or very unlikely the cable fault i mentioned but atm you have the correct voltage and therefore no problem .. a look at the gearbox lead might be in order just to check .
 

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I had the same warning on my car a few months ago, and ordered the whole alternator and replaced it:

Bosch alternator from autodoc.co.uk, Article no: 0 986 047 140, original Porsche Alternator: 997.603.012.03

I found out afterwards, I may just have needed to change the regulator, but i never tried, and it would have meant taking out the alternator, swapping the regulator, and trying it again. If you are that way inclined, I am pretty sure this is what you need:

Regulator Bosch F 00M 144 136, from autodoc.co.uk
 
OK Demort -= I've done it! Was actually pretty easy with the x51 as the airbox leaves it quite open. :D
Anyway, I got 14.7 volts from that lead, using the inlet manifold for earth.

Thoughts now?

Dodgy lead of some sort? Perhaps earth cable or alternator cable?
 
Poker2009 said:
I had the same warning on my car a few months ago, and ordered the whole alternator and replaced it:

Bosch alternator from autodoc.co.uk, Article no: 0 986 047 140, original Porsche Alternator: 997.603.012.03

I found out afterwards, I may just have needed to change the regulator, but i never tried, and it would have meant taking out the alternator, swapping the regulator, and trying it again. If you are that way inclined, I am pretty sure this is what you need:

Regulator Bosch F 00M 144 136, from autodoc.co.uk

Did your warning come and go? Mine has happened twice at operating temps and then goes when the engine is cold.
 
The warning light came on one day whilst I was driving, and then over the next few days, it would come on after a few minutes of driving.

I think I could have got away with just changing the regulator. If I had to do it again, I would try that first, as it is about £30, the new alternator was £320. It is straight forward to swap once the alternator is out.
 
Had similar issue with the waning lights on a 996 a few years ago, but ignored them and drove the final 10 miles home , got home and the battery was hissing and looked like a rugby ball :eek:

I read up on the possible causes of the warning light and replaced the regulator, cheap (£40?) and quite simple DIY which fixed the issue.

Good luck with getting fixed
 
If you suspect the alternator / control unit, remove the alternator and take it to a reconditioning / rebuild centre for starters and alternators. They will test and if necessary rebuild for a fraction of the cost of a new one. I did this with my old 964, which had the alt built into the fan, turned out to be a Citreon unit, rebuilt as new.
 
Ordered a new bosch reg. Am pretty confident that I can pull it out and replace it.

Am going to swap out the lead whilst it is out, so going to research that job now.
 
CarreraMonkey said:
OK Demort -= I've done it! Was actually pretty easy with the x51 as the airbox leaves it quite open. :D
Anyway, I got 14.7 volts from that lead, using the inlet manifold for earth.

Thoughts now?

Dodgy lead of some sort? Perhaps earth cable or alternator cable?

Yup .. you certainly have a lead fault with a drop of that size but i see you are already in the process of replaceing it so ill leave you to it :thumb:
 
deMort said:
CarreraMonkey said:
OK Demort -= I've done it! Was actually pretty easy with the x51 as the airbox leaves it quite open. :D
Anyway, I got 14.7 volts from that lead, using the inlet manifold for earth.

Thoughts now?

Dodgy lead of some sort? Perhaps earth cable or alternator cable?

Yup .. you certainly have a lead fault with a drop of that size but i see you are already in the process of replaceing it so ill leave you to it :thumb:

Thanks for your help buddy! Cable ordered.

Am going to replace regulator as it contains brush pack and is an easy cheap job and worth doing whilst the alternator is out. Have ordered cable. Looks a bit of a ballache to do, but am confident I get it done.
 
Just a quick update...

Although quite hard, getting the alternator out and even replacing the alternator lead isn't impossible. Challenging, but doable.

The challenges for me:
Getting the plenum out. Its a squeeze and I had to remove a plastic trim from the top of the engine bay to allow it to squeeze out.

Removing the alternator. I soaked the bushing in releasing agent 1st, but it still required a few whacks with a hammer to release it.

Finding the legendary hidden bolt behind the aircon pump. Tricky to find, but easy to remove and surprisingly easy to put back in.

Routing the lead is tricky, but not overly difficult either.

However, the biggest challenge I have had is getting hold of the correct regulator.

The correct item code is f00m145651 or F00MA45302 . If you don't get that exact one, the plug on it will be incorrect and its not usable.

I've had the alleged right one from car doc and GSf and neither was correct. There does seem to be a couple of sellers on ebay, although I some how doubt they'll be correct either. Getting hold of one has proved to be challenging. If my new source is correct, I'll buy all of them as they only have 4 in stock.

People on here can then source them from me. No chance of getting one off porsche, they only swap out the alternator as a complete unit. Even bosch doesn't stock them. I ordered one from them, only to have the order cancelled the following day.

Hopefully, the one that arrives tomorrow will be correct.. lets wait and see.
 

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