frf

I had the same problem and it was not at all related with battery or alternator problems. If you are having problems with the ABS (the light is on), since the speedometer receives the speed signal from an ABS sensor (in the ROW cars is the one in the driver's side rear wheel, and I think that in the US is driver's side front wheel sensor) and passes it to the OBC and the spoiler controller, if the signal is not correctly received or there is something wrong with your speedometer, the spoiler light is on and the spoiler stops working and the speedometer goes mad as speedometer.
So, in first place have a look at the ABS sensor and ensure that is clean and properly connected. If so, and in my case, the problem was in the speedometer itself because when the ground cable was connected all the signal being sent by the ABS was vanishing!!! The funny thing is that was a MB electrician that discovered it using an oscilloscope.
So, I had to replace the speedometer with a new one in a very expensive deal. I hope this can help you solving the problem.
Cheers

samba-lee

Yeah, I'm gonna pull the wheel to check the sensor and connections. I replaced one front one last year - can't remember which one now.

I think mine gets its signal from rear left sensor which we just replaced with a new one though

I just came into work to pick up my scope to do more serious signal testing.

Lee

JM993

You should be able to do a system check of the ABS with a Durametric.

My concern is that, as you mention, your shop may have spiked an electrical component when working on the starter.

I hope it's a simple and inexpensive fix.

samba-lee

Thanks for en encouragement.

I've just been out to do some Streather tests.

All the speed sensors check out via the ABS connector so I assume they and their grounds are good. The ABS connector grounds are good, I guess it wouldn't be informing the Central Informer if it wasn't working and the fact that I can read the ABS fault indicates (I assume?) that the ABS module is working in some way.

This is looking more like the ABS controller now. The shop the car was in for the starter has said they swapped the ABS ECU with a known good one as there was another 993 in the shop at the same time and the ABS fault went away!

So I've bought a used one and hope it lives up to its advert - ebay Porsche parts seller so the seller has some reputation to think about. Assuming it's good, then I'll send mine off for a repair so I have a spare...

fingers crossed. If it works then I'll just put this down to coincidence with the starter change and eat it. I doubt that would use a booster on the car - I mean they have F40's, Dinos, Lambs etc. so they are a serious shop.

Out of interest, where is the Central Informer controller as I could check that the speed signal is getting to it and then on to the Speedo, although if I plug my replacement on in and it works I won't care any more...

List price for a replacement ABS ECU is £1400

Lee

samba-lee

Oooh, forgot to mention that when I took the car out today and went over 60'ish MPH (with spoiler extended manually!) the speedo started working erratically and the spoiler light went out.

When dropping below about 60 the speedo stopped working, then started again when going over 60 - it was pretty consistent.

I'm kind of reading this as there being no output signal from the ABS unless input speed signals reach a certain level.

Lee

JM993

Your spoiler issue isn't surprising as its function is dependent on vehicle speed.

IIRC the central informer is under the dash.

Yikes - I would not be pleased with a shop swapping my good ABS controller into another car with a problem for test purposes. In my experience, the ABS ECUs almost never go bad without a little "help" if you know what I mean. It may be worth a discussion with your shop to see if they will pick up the cost of the replacement. Though we have no proof, INMO they screwed up when they replaced your starter.

Anyway, I hope you've solved your problem.

Cheers,
Joe

samba-lee

The Durametric shows the rear left sensor with fault #28 (open circuit or short), same as the shops diag tools. No other faults reported - I suspect the ECU has gone bad on those two pins.


Lee

d ward

They may do top end cars, ferrari, lamborghini etc at your repair shop.
But I agree with jm993, I would not trust them with my car.
Swapping electrical bits from one car to another for test purposes is either laziness or stupidity. If they have test equipment and a scope etc, and they should have if they are any good, then they would be able to test your abs ecu and not have to resort to swapping ecu's with other paying customers cars.

For all you know they could of damaged your abs ecu by using it to fault find on another 993 they had in for repair

samba-lee

So I took a gamble and bought a s/h ABS ECU off ebay for ~$300 - advertised by a Porsche parts dealer, never repaired and 100% working came from a rear ended car.

It came, I plugged it in and all was resolved - phew. ODB shows no errors and no lights on the dash now. The speedo and spoiler are happy too as expected.

I guess that's that then. Weird error.

Maybe I'll put a padlock on mine so no shop can pull it to test another car.

thanks for you input.

Lee

techman1

I am guessing you disconnected the battery before working on the starter.
From past experience with the same type of electrical gremlins, I would take a very close look at the ground cable at the battery. Do yourself a good thing by measuring the length and type (or remove it) and go to the local parts store. Get a replacement and install in the car.

Reasoning: I was informed over time the ground strap builds up resistance, either in the cable or connection, and needs replacement. Yep, you are going to tell me it looks new. Mine did to, but the flashing dash lights stopped immediately after replacement of the ground cable. Yep, it very well may be something else, but the cable was $12 and took 15 minutes to swap.

samba-lee

Yeah, it's on my list and I will replace it.

I jumpered the ground leads on the battery and engine with a set of jump leads - it didn't solve the dash lights issue so I figured it wasn't a ground issue.

I measured the resistance of the battery ground lead - as good as 0 ohms.

Yes a new one is cheap, even from OPC, so I'll do it anyway ready for winter. I'd like to do the starter one as well but it's awkward to get in there especially with a Tip box.

Lee

techman1

See above entry