993MAN

I searched for a few hours before adding this post, but all the ABS failures seemed to be on older cars, 964, 928, and surprisingly plenty on the 996's.
There's hardly any posts about the 993's.
But theres something wrong with my system.
The ABS light comes on and turns off on start up, but there's clearly no ABS. I tried it yesterday and left some black marks on the road, twice, just to make sure.
The pedal never pulsed. Everything else seems OK, I checked the fuse.
Doe's anyone know what to look for or something common, obvious to look for?
Cheers

jdistefa

Could be gunk in the ABS system or it could be the control module. There have been posts re. flushing the ABS system.....

993MAN

Thanks Matt,
The system has been flushed properly. Im going to check the ABS sensors, when I find out what they look like lolol.
My car repaired on the back so I will check there first.
Cheers

Stuttgarter

I'm a former ABS engineer. If anything is wrong with any of the wheel speed sensors, the ABS light should come on. It is hard to think of a scenario that would create your problem. One very unlikely one is that all four sensors are returning zero speed. However, the sensors themselves must be connected or the light will come on, so that would mean that all four tone rings are non-operational. Since the dash light operates normally at start up, we know that the ECU is present and functional. A mechanical fault should also set the light. If there is a valve, pump or accumulator failure, the system will know and set the light. If you have a friend with a 993, try swapping the ECUs. This is assuming they are "serviceable", some of them are not meant to be disconnected from the hydraulic unit, though we did this on a daily basis on development vehicles without concern it occasionally wrecked the ecu so be gentle. PM me if you have any other questions.

mongrelcat

Just a guess, but there may be a mismatch if the shop replaced a sensor: http://www.pcarworkshop.com/images/c...1997_64097.pdf

AOW162435

I have a pair of rear ABS sensors that I would gladly pop in the mail for you. Let me know if your sensors are suspect in any way and we can talk further.


Andreas

Martin S.

They will go nuts if you are having a rear wheel bearing failure, or a axel nut failure. The speedometer will also go nuts. I know this from personal experience sad to report. $1,700 later all is well. Replaced both axels just to be safe.

Another culprit for NO ABS is a mismatch on the tires. The rolling radius delta front to rear cannot be more than 3% (I believe 3 % is the number). I put on 235/40/17 tires on the front and 275/40/17 on the rears...ABS light on immediately...sold the 235/40s to a Bimmer guy and replaced them with 235/45/17....

ppressle

Have you checked for any ABS codes? That should help identify.

993MAN

Thanks for all the input guys.
The sensors look OK to the eye. I took them all out and cleaned and inspected them, and they all looked normal to me.
The rear axle was replaced and the tyres are all standard and havn't been changed (but that's looming)
The ABS ECU was replaced and I can only assume it's OK because the light comes on when you turn the key on, then it goe's out as it should once the car starts.
The speedo is normal and seems fine.
I'm taking the car into an auto electrician on Wednesday to see if all the relays are OK.
It's a bit puxxeling all the same.
Thanks again

993MAN

Just a thought.
Is it possible that if the brakes were not bled properly that this could cause it?

Stealth 993

That was my thought, maybe some trapped air.

I also thought of something stuck on the wheel sensors, but you already checked them.