ABD light

[JB 3.2]

On my C4 the red ABD light comes on occasionaly, usually from start up rather than while driving.

My understanding from the manual is the green light may illuminate during driving at speeds below about 40 mph if traction on one or more wheels is lost, but the red light probably indicates a fault.

Any thoughts on things that I should be checking?

 

[Mark Elder]

Interesting one that because there is so much overlap between the ABS and the ABD sensors and electrics that it's tough to see what can be exclusive to the ABD warning light. I think the "993 Essentials" book talks about some actuators. I'll have a look in the book when I'm home. Can't be the pump because that has it's own warning light.

 

[JB 3.2]

Thanks Mark,

I did a search on the Rennlist site earlier and as you indicate the ABD and ABS lights usually appear together, often because of a loose alternator belt or battery output.

 

[fergusond]

my C4 used to do this, like yours only after starting, but only first thing in the morning, I was told its normal as its the pump building up the loss in hydraulic pressure thats dropped off over night. That was about a year ago, I've changed the brake fluid, bled the brakes (and clutch slave cylinder) since then and I never seen the light come on since.

David

 

[clyde]

That would be the brake pressure light wouldn't it David? Bottom left on the dial? My pressure light comes on on morning start-up for a short while but I don't think I've ever seen the red ABD light on. Except when the fan belt broke and the whole dash lit up like a Christmas tree. The bad news with that was that it had just been replaced by an OPC but the shims on the pulley had not been properly done. The good news is that it broke literally as I was driving into my garage so no harm was done and I didn't need to call on the RAC.

 

[Mark Elder]

From the list of fault codes the following seem to be unique to the ABD (therefore I guess could cause its warning light to come on without the ABS light) - not that this really gets you anywhere - you really need to get linked up to a diagnostic test tool that can say which of these codes you have.

14 ABD intake blocked
15 ABD switch-over valve
17 ABD TP info
34 ABD inlet valve rear right (the other valves are dualed with the ABS - ABS only seems to have one for both rear wheels)
38 ABD exhaust valve rear right (ditto)

 

[JB 3.2]

Thank you all for your observations.

I have established that if I start and drive the car in a straight line then the ABD light does not come on untill I apply a significant amount of steering lock such as on a roundabout. This I presume relates to the inside wheels moving at different speed to the outer wheels.

Can anyone tell me where in the car the ABD unit is located?

Mark did you obtain the fault codes from the 993 essentials book, and if so is the equivalent of the Bentley manual I used to have for my 3.2?

 

[Mark Elder]

John,
The codes are just from the appendix of Adrian Streather's "Porsche 993 the essentail companion" - but this book has been known to be wrong in the past....although I suspect he just cut and pasted these fault codes.

Interesting diagnostic you report....because it points to one of the wheel senors, but the sensors are all in common with the ABS....so why is that light not coming on?

The ABD/ABS elecronic brain is the flat box mounted verically to the front/driver side of the spare wheel. The pumps and acuators are in the box just behind the battery.

 

[fergusond]

sorry about that Clyde/JB 3.2, I was getting my red lights mixed up, the only time I've seen the ABD light on is when the back wheels spin up with poor traction and most of the drive is transfered to the front to pull my car up the steep bank where I live when its been snowing!

regards
David

 

[Guest]

I have a 1996 C2 with a factory fitted limited slip diff. There is an ABD green light on the display, but have yet to see it!
AFN, from whom I bought the car, said that up to 40mph, the LSD was as effective as 4 wheel drive.

Expensive option though.

Regards

Peter Lapukovsky

 

[Mark Elder]

I can get the green light on only by putting one side of car on a river of ice and other side on tarmac (then adding loads of boot from stand still).

What it can't handle (but I wish it did) is the low speed, high acceleration, out of small roundabouts (in the wet). I can quite easily spin both rear wheels together (guess that's the LSD) and wiggle the rear end sideways. The central diff is too slow to react in this situation. Its viscocity does not lock up fast enough.

Awaiting some good ice for some more experiments[]