arjay

Hi all - apologies for posting a second post on similar topic. The other post https://rennlist.com/forums/964-turb...f-problem.html has so many entries I can't get a reply there any more.

So: I am fault testing an intermittent ABS light/alarm warning and a speedo that dies at the same time, on my 1993 964T. So far I have done the "clock repair", re-soldering all fifteen pins on the back of the clock and the five pins on the speedo for good measure. Problem still there.

Now I am testing the R34 relay by bridging pins 30 and 87. Could not reproduce the fault after 20 miles of driving (would normally happen well within that time). So it looks encouraging.

My question is: is it OK to leave the bridge in permanently (when switched off over-night and also when driving for the next few days)? I need to get several good runs in before being sure it is the relay. I have to leave the bridge in when driving as the fault may not happen until after 10 minutes of starting the journey.

Any help appreciated. Thanks.

Metal Guru

Relays are used for isolating low power signals from high power ones or as logic elements.
Either way, they are relatively cheap so you may be taking a risk with the jumper in place.
It's good that you found the issue. Maybe you should have jumpered the relay before you embarked on the soldering job (and proved once again that Man is inherently lazy ).

arjay

Thanks for the advice. I am going to run the car one more time tonight with the bridge just to confirm it is the issue then get a replacement.

As to doing that before the clock, you are quite right - I should have done the relay first. My only excuse is that it was ignorance rather than laziness!! I thought the relay would "either work or it wouldn't". I did some testing with a battery and could hear the relay and also found that as soon as I pulled the relay out when the engine was running, the alarm would squeal like a stuck pig. I thought that meant it was OK - clearly not.

Anyway I nearly moved on to replacing a speed sensor - much more expensive so I feel better about the way things turned out.

I'll try for a replacement relay tomorrow though it's an hour's drive to a Porsche dealer here in Spain and then no guarantee he'll have one - ringing up to check first is a waste of time. May have to source it on the internet. But - then again - will a new one ever arrive via the Spanish post

fritz k.

hi,

as far as I can see in the wiring diagram the relay 34 gives switched + (terminal 15) to the abs control unit and the abs hydraulic unit.
should not cause any trouble if you keep the relay bridged for testing purposes.

I also would have the speed sensor on top of the list and i would start with checking all wires and cable connectors between sensor and control unit.

fritz

arjay

Fritz - thanks for your input. For everyone's information I drove the car for over 50 miles tonight - slow, fast, over bumps and everything else I could think of - with pins 30 and 87 bridged.

Not a single complaint from the light/alarm combo. It is just possible that this is not significant, but on the last 10-20 journeys I have made with the relay fitted, the alarm went off within 5-10 miles. So I am reasonably confident that R34 is the problem.

I am going to replace it and then see what happens. I want to avoid tackling the sensors if i can get away with it.

Just one interesting point - a friend of mine who is an electronics expert had a look at the way the R34 relay was seated in the board. He said there was a lot of play sideways and back/forward. It is just possible that this was making a poor connection, either over bumps or during hard braking.

So, if a new relay cures the problem, I am going to "tin" the relay's connectors with some solder to thicken them and then try the old relay again. If it works I know it was just a loose connection and I have a spare relay for the future

I'll post any results I get.

A big thanks to all who have helped with this problem.

arjay

OK - this issue has been solved after some further problem-solving.

First, I tinned the connectors of the R34 relay with a bit of solder to thicken them slightly. I replaced the relay and tried the car but the alarm/light went off almost straight away - so that was a non-starter.

I finally bought a new relay and since then have had no further problems - at this point I consider the problem solved.

Just to help anyone else coming to this post with as little knowledge as I had. Don't believe what normal diagnostics might tell you - beg, borrow or steal a replacement R34 relay and try that before anything else.

FYI I found that:

1. Removing the relay with the engine running immediately triggered the alarm.

2. Removing the relay and testing by wiring up to a 12 volt battery showed the correct resistances - i.e. no resistance and an open circuit with battery off and resistance and a closed circuit with battery applied.

3. Furthermore, with the ignition on I could remove and replace the relay and hear a relay close further down the line at the abs control or hydraulics unit.

In spite of all these positive indicators, the unit was clearly faulty. Maybe an electronics guru on the forum can explain why!

Now for those of you coming to bridge the relay for the first time - here are a few photos. First, the relay is the largest silver rectangular relay at the front of the fusebox (see photo).

Second, the bridge wire can be any piece of reasonably thick wire with a couple of connectors similar to those on the relay. My effort is in the second photo - it just uses a couple of bits out of an English 3-pin plug.

The third photo shows the bridge in place. You want to bridge connectors 30 and 87. Conveniently, Porsche labels the connectors on the underside of the relay. There is also a simple circuit diagram on the relay for the four connectors, showing which ones make the closed circuit, should you wish to test for resistance.

Hope this helps any newbie who needs a bit of help.

Thanks to all who helped me get to the bottom of this (and saved me the price of new speed sensors etc)

arjay

Sorry - don't know how to mark posts as solved in this forum. Perhaps a Mod could help?

Porsche930

Hello Arjay, thank you for your detailed write-up on troubleshooting the ABS light issue. My 90 C2 Targa recently started having the anti-lock light lighted up intermittently at two different trips while I was driving. The light went on for about a second or two in the last 2 weeks. The light went off after both occasions and so I don't know when it will/may happen again. By the way, there was no bump or uneven on the road when it happened. I am going to check R34 relay and hopefully to isolate if it is indeed the culprit. Again, thanks for all your posts.

arjay

No worries - sorry I can't help any more. Good luck!

Richy

Dear All, just wanted to post something to thank all that contribute information like this to forums,...... to take the time to help others is a great thing, I only hope I can contribute some info that will also help someday.

I had the exact problem laid out in this thread and all the information contained helped me solve the issue very quickly.

Thanks again !