993Godspeed

Today took my 993 out for a drive and stumbled across a problem. my ABD light started coming on and car started to hit the brakes when I tried to accelerate. As soon as I hit the brakes or slow it down to about 5-10mph the car releases the brakes. As soon as I release the brakes and try to accelerate ABD light comes on and slaps rear brakes and starts slowing or braking for me.

I read the code with my durametric tool and said Rear right Speed Sensor was implausible, I assume the sensor needs replacing. I took it out and cleaned it and it was full of grease, I cleaned it and cleaned the hole. Took car for a drive and same problem.... car hits brakes above 10 mph. Whats funny is I read the ABS module and there are no codes now! this is driving me crazy. Someone please help.

I searched various threads and have heard many things, I recently replaced all three front fuses right above the ABS brain so it can't be that. Also cleaned all the teeth on the harness and the ABS brain. Anything else?
Thanks.

C4S993

I tested all 4 and found one speed sensor that was shorted; replaced it and ABS light OFF (yeah).
Read the Ohms across the white connector two-wires that resides in the brake pad plastic protector. The good sensors will read fairly close resistance values while the dead sensor will be way off (relative to the others).

993Godspeed

Thanks. I will order the speed sensor and see where it goes.

C4S993

I am curious what resistance (Ohms) the suspect speed sensor was ?

993Godspeed

I have not read it yet as there is rough weather here in NY, this weekend will get to it. I am hoping that the replacement will fix the issue, if not I suspect either the ABS Module or Brake Booster pump.

C4S993

I found that the brake booster pump takes a min or so to pump up to the correct limit before the lights go off. You can hear the pump working. My '96 TT brake booster pump warning lights are red until I exit the driveway. The ABS Module often just requires reseating it's relays. Getting it's plastic cover off can be troublesome.

993Godspeed

It has to be the sensor...If it were the pump my brakes would not work...Correct? I can hear the pump and all. Also speed seems to be a variable, as long as I stay under 5-10mph the car drives and does not hit brakes for me. The minute it goes above 10 mph or so ABD light comes on and brakes come on immediately slowing the car down.

Cleaning the rear sensor might have been enough to eliminate the error light but probably the Ohms that is transmitting is not strong enough to tell the ABS brain it's functioning properly, also it eliminating the error code.

C4S993

Yes, if you hear the pump that is a $$$big plus ! The bad speed sensors is telling the abs module brain that your in traction control trouble when your not. A false positive sets off a series of drievability problems.

I think the speed sensors are inductance electrically and thus send frequency info to the abs module.
So inductance resistance is somewhat unique in Ohms law.

Bradford

Godspeed, I can't help but notice that you have had a lot of issues with your car since joining Rennlist. Do you mind me asking what the history of your car is?

993Godspeed

Brad,

Sure I definitely don't mind disclosing it. But honestly not much trouble since I am ok with the wrench on weekends.

Only issues I have had were a bad turbo, bad MAF and misfire codes which were due to Bad plugs and maybe bad injectors when I first got the car.

The car was hit in the driver side, not much damage but enough to require a new bumper and driver side light. After the incident it was parked for an extended period of time, i'd say at least 6-7 years without turning the key. I bought it and fixed it, resprayed it and have never looked back. Best buy I have made in my young life

Car has been to quite a few track events and I have made a few mods such as PSS10's, BBS E88's, 60lb injectors, Tial GT30's with Protomotive tune & Status Racing seats.

Motor is rock solid, only has 50K miles and I have not had an issue with it. I am currently in the process of building it and she will be put away for some time until my build is done.

Here is a side pic, my daughter calls her the Baby blue whale.

Bradford

Thanks for the background and good luck!

993Godspeed

Finally got around to installing the wheel speed sensor, unfortunately same problem occurs. My tech advised for me to disconnect the ABS computer and drive it to see if that helps. Lo and behold car drives perfect again. Seems I need a new computer, car stop perfectly and I could stomp it again . Will replace the computer and take it from there.

lopro

interesting thread, I like the abd threads, what colour is the sticker on your computer?
remember to match the sticker colour apon replacement