arjay

Hi all.

I have a 1993 964 3.6T. I have an intermittent ABS light/buzzer warning that comes on once or twice in a 30 mile trip and perhaps five times in a 100 mile trip but then not again for 3 months. I have read about 60 posts mainly in the main 964 forum but not here in Turbo-land.

I have read about and am contemplating the clock repair suggestion. Before that, can anyone help troubleshoot this set of symptoms - and advise anything less drastic to check before a "clock job". I could do the clock repairs but it is at the top end of my possible ability. OK:

1. Occasionally, when starting the car first thing in the morning, the ABS light will come on after 100 yards and the buzzer will sound. Light goes off 10 seconds later - presumably when system is pressurised?

2. On a trip from Spain to Portugal (800 km) the light/ buzzer combo activated. I cancelled the buzzer but the light remained on. The buzzer then went off another 5-6 times. The light only went out after a restart at a coffee stop. Coming back on the same route I had no problems at all.

3. I was about to try the clock repair but with no further probs for 3 months I got cold feet. Now the problem has started again. But now, the light comes on and the speedo goes off simultaneously on about half the occasions. The computer trip also stops functioning. On the other half of faults, only the light illuminates - speedo goes on working

4. For no apparent reason, the light will also sometimes go off after another 10-15 minutes of driving and the speedo start working again - only to "die" again 30 minutes later! It is not apparently activated by hitting bumps (of which there are many in this part of Spain). I understand that the speedo gets its signal from the ABS system

5. I have an almost new battery and the alternator was replaced relatively recently (well before the ABS light problem). I am pretty sure that the brake fluid reservoir is up to the max level but will check again tomorrow as it seems to be a key factor.

Thanks for any help you guys can offer

Vincent C.

did you solve your problem ???

arjay

Actually, I didn't get any replies here or in another forum - so wasn't sure exactly where to start!

I can't do anything until Saturday but will see if I can find the two front abs sensors and check resistance on them. I'll also clean up the grounds etc.

As far as I can see from other threads, my chances of getting the actual sensors out are pretty slim - they seem to inevitably corrode themselves in badly. I can't afford to take the car to a Porsche dealer at the moment. Anyway I am used to just reaching down and cancelling the alarm; can live with the light on as well!

Let's see where I get to on Saturday.

Thanks for your concern

rizij

If I understand the problem, try checking the connector block of abs in the trunk, I was like when there is exposed to water and oxidized contacts.
sorry for bad English))

arjay

Thanks for the reply. I'll work my way back up from the sensors and look at the abs connectors as you suggest.

By the way - you have no need to apologise for your English. Mine is not very good sometimes and I AM English

Vincent C.

might check the relay as well...have seen a bunch of those go bad....vinnie

arjay

Ah - my ignorance will now show. Where would I find the relay?

Unfortunately I only have a German manual for the car and no workshop manual or other books. Using the car three days a week, I never had time to do any work myself. But now I have bought an old Hyundai Accent to get around in so I can do more work on the Porsche. Boy, have I a lot to learn

Vincent C.

it is a tall slim silver relay in the front row....its should be the only silver relay in the front row....starts with a 928 part #.....you could jump 30 to 87 and see if the problem goes away....vinnie

arjay

Sorry - in the front row of what?? Told you I had a lot to learn

Vincent C.

in the fuse panel....in the bonnet.....

arjay

Thanks Vinnie. I wondered for a moment if it was housed somewhere else - in the ABS system - near the ECU or whatever. I'll start in earnest on Saturday and report back.....

arjay

Progress report and a possibly significant finding

Since this is an intermittent fault, and as the light is currently not coming on (typical!), I decided to follow up troubleshooting leads from many posts on the subject. Hopefully I would find something significant. Here is what I have done so far:

Brake Fluid
a) Checked level and it is exactly at MAX with engine running and a few pumps of pedal.
b) Checked and cleaned float under filler cap - moves and clicks smoothly.
c) Removed, cleaned and reseated connectors on top of filler cap.

Battery
Checked voltage of battery. Ignition off - 12.34V. Engine idling - 13.96V. Battery warning light is on when key is turned but goes out immediately engine starts. Does not come on when idling. Figure that's OK.

ABS Power Supply
The ABS system gets its supply from a second lead attached to the +ve battery terminal. Some say this can come loose, fray and/or corrode. I removed the terminal connector, cleaned the connection, checked lead was in good condition and replaced - tightening firmly.

R34 Anti-lock Relay
Started car up. ABS light comes on when ignition is turned but goes out a few seconds after engine starts. I removed the relay and re-started engine. ABS light stayed on and alarm sounded. Put the relay back in. Again light stayed off/no alarm when engine started.

To duplicate hitting a bump: with the engine running I wiggled, lifted, pressed down on, tapped sharply, and pushed relay from side to side. It rocked quite easily but I was unable to make the light come on - i.e. connectors seem well seated. To be on the safe side I removed relay, cleaned connectors and reseated it firmly.

Front wheel ABS sensors
a) Uncoupled the white front sensor connectors from the black cylinder (see first photo). Tested the resistance across the terminals in each front sensor. Results: 1.044 KOhms on right front and 1.041 KOhms on left front. Unless anyone says different - I take it that the two sensors are working correctly as these figures are all but identical to each other and in the range reported elsewhere. Reports of faulty sensors state that resistance shoots up to figures like 27 KOhms or 10-30 times normal.

b) While here, I removed, cleaned and reseated the connectors for the brake wear sensors on each side.

c) Unable to remove and clean the sensor grounds on either hub. The hex nut, which holds the sensor on, and which also bolts the ground to the hub (brown lead), was well rusted and could not be moved. (same on both wheels). I did not want to end up breaking it off as has happened to OPs with same problem. If I have to change the sensors then I'll have to anyway.

d) When I came to reconnect the right sensor plug I found what maybe a significant development. One of the metal tubes which forms the female side of one of the connectors had sheared off and was lying loose in the plastic plug. It fell out when I was measuring the resistance. This "tube" should connect to a piece of metal at the back of the plastic plug but it is possible that the connection was not being made reliably - hence an intermittent fault.

The first photo shows the two plugs (wear-sensor and ABS sensor). The female parts of the connectors can just be seen in the left-hand plug. The second photo shows the broken piece of the metal connector.

This plug is welded to the short piece of cable and presumably is part of the ABS sensor assembly and could not be bought separately. I thought of trying to get one second-hand or otherwise repair this one but have not got much further than that yet.

I jammed a bit of silver paper down the hole and forced the broken piece of tube back in - then pushed the white plug back into the male as firmly as it would go.

I just can't get the abs light/alarm to come on today on a short drive. The task now I suppose is to drive the car until either the light comes back on or I presume it is temporarily fixed. (And in the meantime investigate a more permanent repair for the broken connector).

Other things not yet tried:

ABS Valve Unit
The whole of the boot (trunk) area is immaculate on my car - not even a scrap of dust. The valve unit looks brand new and I can't spot loose or dirty connectors inside it. OPs have said that this unit does not normally cause any problems so I have left it alone.

ABS Central Unit.
I have yet to identify this but am going to look again and check for dirty/corroded connectors here..

Thanks for all the help people have offered.

John McM

Try the links in this thread for some docs that will help you with the car.

https://rennlist.com/forums/964-turb...-good-one.html

Big Jock

Simple question.Have you made sure the abs/speedo fuse is ok?Not sure what nr it is but it was blown on mine and speedo didnt work and abs light on permanently.

arjay

Good point. I did check the relevant relay - R34 to be exact and that seemed OK (see earlier post in this threads). Bt not sure if there is also a fuse or not? Since the damn things keep coming on again for a while before dying again, I'm not sure that a fuse would do that?

I am going to change the sensor and see if that helps. I am also going to pull the clock and see if I can find any loose/suspect connections there. Seems to be a frequent cause of intermittent faults.

Thanks for your thoughts.