Failed ABS....how do I diagnose?
 

When I was doing a complete flush on my brake system a while back beause I was replacing the lines, etc., I got some air in the system and I think it has led to my ABS not functioning. I ultimatley bled all of the air out of the main lines and the brakes themselves seem to work fine. However, I get some lock-up on very hard braking and never experience the pulsing in the pedal like I'm used to with ABS. I understand that a bleed involving the hammer may be required to exercise the ABS. Is there any other way to accomplish the same thing or do I take it to a shop? Is there any damage I could have caused that I need to be aware of?

After doing a little search, maybe I don't know why. I've been assuming it's air, but after reading some threads on the C2, it doesn't seem that ahammer is required for a brake bleed. Now I simply don't know why they lock up & I don't get the ABS pulse. Does the whole system shut down if there is a sensor problem? FYI, I do NOT get a brake dummy light on the dash.

Oddly enough I experienced something similar out on the track on saturday. No pulse, lockup under very heavy braking.

I used to have an issue where only my right rear would lockup, thought it was the ABS controller but considering it is only three channel that didn't make sense. So I swapped out the 2 piston for 4 piston and that resolved it.

Now my fronts seem to lock up from time to time. I do have functioning ABS cause I can feel subtle pulsing from time to time but can still lock them up.

I don't know if I will just slide for eternity cause out on the track the second I felt that I obviously start pumping! Thankfully no real issues but sure scared both me and the poor instructor :)

-Dave

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'91 Strosek C2 (supercharged)
'00 Honda S2000
'04 Honda Element (hey need a practical car for New Hampshire)

Lock up is the symptom that I have had in the past with air in the ABS hydraulic unit on my 944 Turbos. I certainly think that air in the 964 ABS pump would cause similar problems. Usually a very thorough bleeding will fix the problem.

I need to bleed my brakes anyway and I'm changing out my cooked front rotors, so maybe I'll do a more thorough job this time. I also talked to a guy over at TPC who said that sometimes when the wheel bearings go up, it can cause some rocking in the wheel speed sensor gear that will make the sensor not work properly. If a thorough bleeding doesn't help, then I think I'll be taking it to a dealer.

Hummmm I bled my brakes big time (full can of blue fluid replace) last week. But will check again just to see if perhaps that was the cause.

I know that my instructor didn't like the pedal feel on my brakes but I don't know any difference since this is the only 964 I have driven (with the crazy downward pushing pedals hehehe).

But RedRS let me know if the bleed solves your problem. I will continue to hunt on mine.

-Dave
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'91 Strosek C2 (supercharged)
'00 Honda S2000
'04 Honda Element (hey need a practical car for New Hampshire)

I did a thorough bleed over the weekend and my brakes are still locking up. My ABS light comes on when I start the car and then goes out, so there is no obvious fault. I also checked the ABS fuse and it seems to be fine. My current list of culprits include wheel speed sensors on the hubs (to be removed, inspected, cleaned and reinstalled), ABS relay, ABS pump (ack!)...and what else? Is there any way for me to diagnose what is the problem?

At last I find people with the same problem as me! my '90 944 turbo does exactly the same as described by RedRS - ABS light comes on at startup, goes off, can hear pump self testing as you drive off, heavy braking causes lock up -no ABS brake pedal pulsing(can hear pump run briefly) ABS light stays off.
My car has done this since I got it over 2 years ago! It drives me mad I go through periods where I forget about it but its annoying me again! I have made many attempts to fix this: Bled brakes many times , sent Hydraulic unit for test- no fault found ,fitted used ABS ECU and Hydraulic unit from breaker yard - no better. I have even gone as far as connecting an oscilloscope to the solenoids while testing the brakes, I can see that there are voltage pulses being applied to the solenoids but still no ABS action
If I deliberately unplug a wheel sensor I get the warning lamp on so I know the system is trying to work.
Oddjob did you find a reliable method for bleeding your turbo? If thats all it was I would be very happy!
If you search the archives there are handful of similar stories from 911,928 and 944 owners most seem to be unresolved ,Sorry I can't offer any solutions for now but I'm keen to hear if any of you manage to crack it! -K

When I had lockups fellow rennlisters advised me to clean the wheel sensors and it solved the problem completely:)

http://i32.photobucket.com/albums/d2...y/P7070801.jpg

http://i32.photobucket.com/albums/d2...y/P7070805.jpg

Steve, when your sensors were dirty and you had lockups did you also get the ABS warning lamp coming on?

Not during the lock up but sometimes I had the warning lamp come on just after I started the car and moved off. It would then go out after a few seconds. My locking up was intermittent which mirrored the warning lamp being intermittent, if you see what I mean? Since cleaning all four sensors and vacuuming out the sensor holes in the hubs (easy job) I have reliable ABS and no warning lamp.