Warning light scare

Just been out for a run in my 98 996. It's just had its engine rebuilt (Harteck) and is a joy. I was out on the local dual carriageway today and overtook a slow driver. I accelerated quite hard and my TC off slight came on. This was followed by the ABS warning light? The volt gauge went up off the scale and the battery warning light also came on? The air conditioning turned itself off but running temperature stayed consistent. When I got home (a minute away) I checked to see the belt was on - it was! I've let the motor cool for a couple of hours and started it. The TC and ABS lights have gone off. The battery light is glowing? Any ideas what this might be? QM

Probably be the voltage regulator?, what ever you do don't drive it - or check the battery first. I drove on when I had the same lights come on and when I reached my destination the battery was hissing away and shaped like a rugby ball! Easy fix IIRC voltage regulator about £50 Bosch item , you need to get the alternator out and it fixes to the back of that. Quite an easy DIY - think the only tool I didn't have was a large socket to move the tensioner 24mm. Porsche will tell you to change the whole alternator but the regulator replacement is an easy switch.

Thanks for your reply vlad. I'm curious as to why that would impact on so many things driven by the belt? QM

i'm with Vlad here , alternator and an overvoltage .. as every components requires 12 volts .. well 13 to be exact then an over voltage will cause many strange issues .. pretty similar to an undervoltage really . i would start by doing a vehicle scan for any fault codes , i expect there will be some , with a fault code you get extra info on top of the code .. it will often say voltage , engine temp etc etc .. looking at the voltage when a fault code happened will help . second test .. a volt meter on the battery . i think that with the alternator light on all the time it also indicates its faulty .. thats an internal short or diode failure . Only other check as its been recently worked on would be to see if the engine earth strap o/s/r and behind the rear wheel is tight .. if left loose that might cause issues but for my money the alternator is the likely suspect .

Hi agin, i've put my durametric on it this morning and it gave the following codes: P1601 Supply voltage exceeds limit value (Engine Module) P0740 Solenoid valve conv clutch (Transmission) 4802 Undervoltage (ABS) 24 Power supply (terminal 15) fault (Air Con). I've got the aletrnator off. In the process i've broken a coolant pipe junction/ bracket! it connects two small bore coolant pipes. The lower of the two pipes is probably only 8 '' long and runs just behind a tensioner pully and connects with the a casing. A few questions: i obviously need to replace the junction/ bracket i've broken. I can see no reference to this on the coolant diagrams on line - does anyone know what this bracket/junction is described as (or part no) so that i might locate one for replacement? I'm going to replace the three pulley tentioners whilst i'm about it. Two came offf easilly. The middle one with the 24mm hex nut wont budge is this a left hand thread? Should it be that tight? How shoukd i test my battery to check if it's damaged - or is this a specialist task? QM

You have fault codes for an over and under voltage supply , that may be the alternator .. it could also be an earth strap .. either engine or battery .. both of which are rare faults but possible . i know the pipe thats snapped as ive done the same .. dam things are so brittle these days you only have to breath on them for this to happen . Im afraid ive been unable to find a part number but a quick phone call to an OPC parts dept should soon get you the part number . The tensioner one .. 24 mm one is dam tight .. if it makes no noises when you spin it then i wouldnt replace it .. link below shows you have a bolt on the back side of it .. 15mm i think but a bitch to undo , that much i can tell you !! https://www.deroure.com/diagrams.asp?TBL=2515&MAK=3&MDL=25&SMA=0&SMO=0&ST=&SC=0 Battery test .. i would have started with a voltmeter on the battery , check voltage on idle with no loads then turn on headlights main beam , heated seats , fog lights ... everything basically and again read out the voltage . To test a battery itself and you need a dedicated load tester .

Hi deMort and thanks for your really helpful reply. I'm going to try a recon bosch alternator. I'll also have one more go at that tentioner. I'll try an OE parts dpt for the bracket - I know i'm going to wince at the price! Interestingly, i saw a 'you tube' video on taking an alternator off - after the event. That clip mentioned the very high likleyhood of it breaking too! QM

Right, recon alternator is here. Went to fitit and it's too tight on the r/h fixing! There's a bush with a thread inserted through it's centre in ther rear of the alternator casing. That's fouling the engine casing which it should fit through! Now, do i heat the alternator casing and try to tap the bush back (giving greater clearance)? Or do i attempt to grind the surface of the bush to give that same clearance? If i choose the latter it's not going to be ground level. Will that matter? QM

Ok .. the rear bush . you need a large socket to cover it .. 22mm i think or a 24 mm .. Insert the bolt into this bush , socket on the bracket to support it , bush will be inside the socket when it moves .. hit the bolt to knock back the bush . if you don't support the alternator bracket with a socket it will snap. socket on the floor , alternator on top and support it on the bracket .

Hi deMort, i followed your advice - it worked and i've got in on, pending bolting etc (to be done at weekend when i have time). Just a question - I got myself a multimeter and put it across the battery. It gave a reading of 12.92. Would that be right? QM

If the engine is NOT running then thats a high reading .. a battery just off of charge would read approx 12.5 volts . your voltmeter is suspect at this point , i have a few so i can check this against another voltmeter at work . If its been on charge then fit it , headlights on for 30 secs and it should read 12.5 volts . More importantly though ... Engine running .. no load .. and you should get approx 13.6 volts .. turn on the headlights , main beam , heated seats .. anything electrical and you should have at least 13.2 volts ..13.4 is optimol .. anything less than 13 indicates a worn alternator . In this case i would replace the unit .

Thanks deMort. The battery had been off the car for a few days before I took that reading. I've now put in on my motorcycle trickle charger. Alternator going to be bolted up on Sunday so I'll take some readings then. The multimeter was £5 from QD but the greatest challenge is my use of it! QM

Im dubious at how accurate the voltmeter is atm but refit it all then test the voltage with engine running please and post results . best to do an idle check with no loads .. then turn on lights , heated seats etc and read off that voltage . Voltmeter set to 20 volts .. that's the standard for one of these meters anyways .. don't set it to millivolts . If unsure then take a picture of the meter when testing and post .

Hi deMort, i've finally got the recon alternator on and replaced all the tentioners. With the battery (pre charged) on the car but with the engine off (no load) it gives 13.10. With the engine on (at idle) with no load its giving a reading of 14.68. With the engine at idle with a load (lights, radio, rear screen heater and heater per ce) it's giving 14.31 Do you think the battery is ok and will it be ok to run with it? QM

I think your volt meter is over reading by about 0.5 of a volt .. taking that off of all your figures and its working just fine . I assume you have no more alternator light on ? just for the record then anything below 15 volts is ok .. different battery states and wiring can give different charge rates .. along with how accurate a meter is as well i would drive it and see how you get on .. any problem with the battery and it will go flat after 3 days or so if not used but that wasn't the original problem so it should be fine .