Porsche Enthusiasts Club Forum

good evening guys, i picked up my 928 s4 today from Wales. Its a 1986 with 122,000 miles

it drove really well and when i got home i filled her up with fuel, i did 225 miles and cost £60 so im really pleased.

when i went to start her the Central Warning Light came on and i had to get her towed home.

Any ideas what the problem is

Thanx for looking Mark

Hi

When you say the central warning light , I assume you mean the big one in the centre console ??

If so then it usually does not come on on its own...it usually comes on in conjunction with a dash warning light... did you have another warning light on, on the dash and if so which was it ?

Also what symptoms did you have....i.e did it turn over, did it have ignition lights etc etc ??

To help we need as much information as possible ?


All the best Brett

Hi Bret, she was fine until i stopped to fill up with fuel

i put the fob on the immoblizer until the light went out, then put the key in the ignition. As soon as the ignition was turned the canceilling button was on.

the engine wouldnt turn over.

i looked in the book and its says " if its priority 1 Brake fluid level, Oil Pressure or oil level it need sorting out immediately and cant be re set

the brake fluid looks fine
i topped the engine oil up as it was between the 2 notches on the dip stick.

i even undone the positive on the battery

nothing helped

i didnt notice any other light were on, on the dash

i hope this helps, many thanx Mark

Hi Mark

Its your immobilizer...

They play up a LOT

Regarding the central light....the way you are reading it is wrong... what it means is... when the central light comes on WITH another light such as oil pressure as an example...you cannot turn off the light by pressing it UNTIL you have cured the problem...then it WILL turn off.... so as an example lets say your oil was REALLY low say by half a gallon or more...you would get the central light go on PLUS the low oil pressure light on the dash....then you would put in a lot of oil and BOTH lights would go off.... and by the way thats NOT your problem as between the marks on the dipstick is fine....nothing to worry about...

So..as it wont turn over its either your immobilizer (id bet money on that) or possibly a relay or electrical problem stopping the starter motor turning over...if it is the immobilizer, it may well start next time you turn the key due to sods law...but you cannot rely on it so you will have to get it sorted out...

Oops just had another thought...if its an auto, it wasnt in gear was it as that will give the same results...no turn over.....it will ONLY turn over in PARK or NEUTRAL...

All the best Brett

Bret, many thanx!!!
no she was in neutral.

Ive got another imobilizer key, should i try that?

i guess its down to finding a good auto electrian (sorry cant spell)

I just hope it gets sorted out quickly

All the very best Mark

Hi Mark

Try the other key, if not auto electrician....

All the best Brett

Bret, Many thanx i will try it before work in the morning

All the very best Mark

Brett is of course spot on about interpreting central warning light.

I would also suspect immobiliser.

It could also be something much simpler, like the tightness/condition of the ground strap attached to floor of hatch. Check that this is tight and clean. A simple electrical problem would fit better with central warning giving spurious indication.

Also check condition of wiring and plug at the post next to the jump post at front right of engine bay (the post should have blue screw on cover). I'm not certain but think power to the solenoid of starter motor routes via here. Poor condition of this plug and its pins is also responsible for many otherwise puzzling 928 electrical problems.

Oh and most 928 no-start problems are fixed by replacing either the injection, ignition or fuel pump relay with known good one (they are all standard 53 relays, so you can temporarily substitute your horn relay for each in turn). The relay chart is in your handbook and handily on chart which should be attached to back of wooden cover over central electric panel in passenger footwell. However failure of any of these relays would not prevent engine cranking at least.

Bret and Stratfordshark,
Thank you both so much I tried the other Imobilezer key, but with the fuse box cover off. When i tried to start her their was lots of noise coming from the relays. So i pushed them all in and checked the fues were in tight and hay presto SHE STARTED

Ive given her a clean and been out for a drive to a pub where Essex Classics meet every other Monday eve and she was faultless, im smiling again

I will post some pictures on here soon.

All the very best Mark

Oh i forgot to mention, the auto electrical guy never turned up

Glad to hear you got to the bottom of the fault in the end!

It's good practice on 928s to replace or clean up all the fuses and relays in my experience!

Next time you get a spare hour or so on a warm day, pull all the fuses and relays one by one and rough up the contacts with a bit of emery cloth. This will solve any daft future issues such as the above plus it will help you familiarise yourself with the fuseboard

Happy motoring buddy!

You have to be careful with anything abrasive, as it can remove protective plating (yes I know this is ironic given that the old contacts can look cruddy!).

Instead of abrasive, you could use squirt of contact cleaner available from Maplin and other places. The basic quality of many 928 parts is such that they will often come up like new with little effort in cleaning.

Anyway great that you fixed problem. Was at Shugborough show at weekend and a guy was telling me how much he fancied a 928, but had been put off by stories of electrical gremlins. As you've found out many of these "gremlins" are simply function of 928 having many powered and sophisticated items (for their day), and what 25 years will do to any electrical contacts. The vast majority of "gremlins" are cured by simple cleaning/refurbing of central electric panel items as you've found, cleaning of all the ground points and earth straps around the car, and cleaning up the 14-pin power plug at front of engine bay. Not rocket science at all. Even faults with various ECUs can often be cured by reflowing old solder joints, rather than having to replace any failed component.

Thank you guys, I will take the fuses and relays out and clean them all. I must admit I was a little bit upset with my new baby, but I love her now!

I've changed the oil and filter this evening, she's sounding much happier and so am I lol

I was trying to get the windscreen washers to work but it sounds like the pump isn't working.

I found 2wires that have been cut off at the passenger side water outlet on the bonnet, what were they for?

Sorry guys another question, how do I get a copy of the fuse/relay diagram? As it's missing from the back of the ply panel.

Thanx guys Mark

Hi Mark,

Can you provide more detail on the cut wires? They may be related to your non-working washer pump...

Fuse/relay charts here:

https://www.928gt.com/skin2.htm

At top left of page under tips/links select 928 fuse/relay charts then be sure to select your model year.

Hi stratfordshark,
i will have a look at the Fuse/relay chart THANK YOU!!!

The wires look like they have been cut off the bottom of the water jet under the bonnet,i found the wires under the black plastic pannel.

Atb Mark

Wires that look like they came from the jets are unlikely to be anything to do with the pump and are possibly to heat the nozzles.

There are several one-way valves in the tubing for the washer system, both these and the nozzles can get blocked. Perhaps you can test the pump with the tubing disconnected to find out whether it works but is too weak to overcome a blockage.