Help, I just bought myself a 89 C4 and had her into the shop to check why the ! light kept coming on and off intermittently and was told that the 'Four wheel drive control unit" and pump had failed. Could this be true and does this light actually cover this fault? Is there any way of verifying this i.e. any other checks to confirm this diagnosis?

Kris
89 C4

 

Hey Kris,

Sounds like you are still having difficulties with that vehicle. I'm sure Adrian will be able to help you sort this out. He seems to be the resident guru on the C4 and it's quirky ways. He certainly has helped me out with some of my "issues". Some of my "issues" he can't help me with. I need psychiatric help for that.

Good Luck. Sorry I don't have any good info for you.

 

Yup, He's the man! Adrian I'm a newbie here but ever since I've picked up this 964 I've been religiously researching it and you seem to be the one who knows this car better then anyone and who keeps helping people out with their problems. Would appreciate your input here friend plus where I could pick up info and stuff to get to know my 964 better. And like slant I have other issues but I guess that's for a whole different forum!

Kris
89 C4

 

Dear Krish,
First thing to point out. What "MAY" be playing up is your traction control system. NOT the AWD. This is purely mechanical. It is fixed 31% front and 69% rear with Traction control offline.
Your mechanic from the comments you have made I do not think knows how the system works. However my help is limited until you give me a description of the lights. "WHICH" lights are coming on and when.
After you start up the Red Warn Light on the top right of the cluster (PDAS or Traction control warn) should be on along with the brake pressure/fluid quantity light centre bottom above park brake light for around 30-60 seconds after the first start of the day. The brake system has to pressurize.
The combinations of lights coming on and when is critically important. The most common problem is Low Brake Fluid Level. I would chzeck this first. Please tell me the lights and when though. Do not allow them to change anything or do anything until we have looked at the problem more closely,
Ciao,
Adrian
911C4

 

Dear Kris,
I was interrupted. I am at work so I spend 10 minutes doing work stuff and then 30 mins doing Porsche stuff.
Anyway, it is easy to test your brake hydraulic pump. Do your brakes work. I am sure the answer is yes. To confirm operation of the pump what you do is with engine running but not going forward pump your brakes hard three or four times. The brake pressure warning light will then come on. You will then hear the pump in the front crank up and after a few seconds the light will go out. If this happens then the hydraulic pump is working. Without the pump you only have have effectively ten brake applications. This pump operates ONLY when pressure is low. It is an intermittant operation pump not continuous.
I am pretty sure your pump is working.
Another check I would like you to do for me is to just turn the ignition on and ensure that the PDAS Warn light, ABS Light and Brake Pressure light illuminate. I have described two of these above already. You cannot miss the ABS warn light.
Please reply with accurate answers to my questions. This will help me help you and ensure you do not waste too much money. One last and very important question. When thelights come on, does the warning horn go off.
Whilst I think about it. On the centre console is a yellow light. Next to the traction control program selection ****. If this yellow light is flashing on and off sometimes, this is quite normal operation. Is telling you that things are actually working.
Ciao,
Adrian
911C4

 

Dear Adrian,

Many thanks for the tips/info. The car's in the shop right now and I have told them to hold everything. I'll be picking it up tomorrow after which I'll go through the check list you've provided and then get back to you.

Thanks man!
Kris
89C4

 

No problem. Do you happen to know the PO of this C4. Please email me off the board with the answer if you know it.
Ciao,
Adrian
911C4

 

Good Morning Adrian,

I think I'm in trouble! Most of the lights don't seem to come on (car not started, but ignition on)! These are the ones that do;

1. Handbrake
2. Brake pressure
3. Circle? (left of handbrake light)
4. !
5. Check engine
5. Charge (intermittently, sometimes it's on sometimes it's not)
6. Seatbelt.
7. PDAS light (four wheel drive symbol?).

I don't have the owners manual on this car (but have ordered it) so I don't have a clue what should be on and what shouldn't. I can see other lights set into the dials but as they don't illuminate I don't know what they stand for. The ABS light doesn't come on but strangely enough I did feel it work when I had to brake hard once and one side of the car was in a patch of dirt.

On the checks:

1. First start of the day, brake pressure light on but no PDAS light and no ABS.
2. Once car has been driven and stopped, turning the ignition on (but not started) causes the PDAS light to turn on for 3 seconds then it goes off.
3. Starting the car causes the brake pressure light to go off.
4. Pumping the brake pedal with engine running doesn't cause the low brake pressure light to come on or the pump to run.

I asked the mechanic to point out the location of the failed components and he pointed at something and called it the pump but it looked more like a valve (solenoid valve?) to me. It was attached to the transmission, it's about 25mm in dia and maybe 75 long with what appears to be a hydraulic line running into it. His diagnosis of the failed control unit was based on the fact that his tester said so and that once he had swapped over a unit from a 993 that was in his shop it showed no problems. Plus my ! light didn't come on any more once he swapped it over. With my control unit in place, the ! light itself comes and goes as I'm driving. Sometimes it doesn't come on at all. When it does it seems to come on when I'm slowing down and then goes off once I'm cruising again.

So that's the summary. I can confirm your initial diagnosis that it's the traction control and not the AWD that's failed but not much else. Accelerating hard on a skid pad had all the wheels spinning before gaining traction.
I think the warning horn has been disabled as I haven't heard it come on at all. Turning the traction control **** doesn't seem to do anything i.e no lights come on etc.

Really appreciate the trouble you're taking here Adrian to help me sort her out,

Thanks and regards,
Kris

P.S. What's a PO number and where can I locate it?

 

Dear Kris,,
Firstly I am afraid you do not have a good mechanic. The 993 unit cannot be installed into a 964. It is a completely different unit, programmed differently. The PDAS control unit will always show up failed when tested with a Bosch Hammer. It cannot ever decide if it has failed or an input has failed so it logs both. Use of the Hammer is also critically important. Correct software, correct adapters and the maint manual.
The PO by the way is not a number but it stands for the Previous Owner of the 964.
So let us get back to your problem. This is going to be tough to work out because something is terribly wrong here.
Sounds like the warn horn has been disconnected OR the Central Informer mounted on the steering column has failed. Your first start of the day lights are correct. 4 is the ABS You will not get ABS unless it is activated failed. You never want to see the ABS.
When the ! warn light comes on the horn should sound.
I will ask you to do the brakes pumping again. You have to pump hard for three or four many more times. Normally 4 does the trick. Try without engine running (makes no difference at all, except having the engine running helps withthe electrical load) you can hear the pump easier.
The PDAS computer plays no role in the running of the brake hydraulic pump system.
I have many other ideas of course but this will just bury you. The warn system is not working properly and this has to be looked at first. I also have a bad feeling that some or all of this is previous owner induced to ensure a sale. This has happened before. I hope I am wrong but this is simply not correct basic operation.
If the traction control programme does not activate (must be under 40kph by the way, it shuts off at 40kph) there is something seriously wrong with the PDAS/ABS Control unit. I have a spare one which works in my basement.
Tough, I really do not know where to go from here. Let me tell you what I think. I think the warn horn has been disconnected and I think the system has been disabled deliberately.
Open the trunk. Remove the carpet. Looking from the front go to the left hand side. You will see on the bottom at the front near the spare wheel a control unit with a big connector on the top. This is the PDAS/ABS Control unit. A little further on and slightly higher on the left hand side you will see a gold assembly with a plug mounted on it and a round device with lots of pipes coming out from it. This is the solenoid valve. I suspect that this valve is shut all the time. It has been disabled to stop hydraulic pressure being applied to the system. This is why the brake pressure cannot be dropped, your system is closed off. This is also why you get a PDAS Warn. This means system is not available due to lack of pressure. I suspect the ABS wartnlight has been removed or disconnected.
You do need an owners manual but that will not help in fixing this problem. Try the traction control programme again. This time do it when stopped. Turn **** right to activate it. Do not hold there. Just turn it right and let it go. The yellow led should start flashing. To turn it off, accelrate to 40kph or turn **** to the left and release. I also recommend you start emailing me at
adrian.streather@rheintalflug.com I can deal with the problem much easier and quicker via email.
Ciao,
Adrian
911C4

 

Krish,

Finding a good mechanic can be very difficult. My wife lost thousands of $$ on her 928 having the wrong things replaced to fix engine and electrical problems till she found a good mechanic. Also - The Dealers are not necessarily better than the independent shops.

My suggestion is contact your local Porsche club and get some recommendations on good Porsche mechanics in you area.

My experience is that there are many really good Porsche trained mechanics working for independent shops and your Porsche club usually knows where they are.

 

Kris, Adrian,

As someone interested in this topic, could you please continue to post on your progress rather than deal with it via e mail - it's interesting stuff and a great place to learn.

Just a request - I understand if you feel it is not appropriate

Thanks

Andy

 

I agree with Andy. I'd like to hear this discussion.

 

Guys,
The reason I ask for this to go to email is because my posts are going to be long and there is a huge time zone problem here. I do not spend all my day monitoring the bulletin board. It is too expensive. I would like to ensure the results get to the list. Allof this is written on tech articles (by myself) in the tech section and in the archives. I like to have a troubleshooting flow and do it in real time. I cannot do this in this forum. However if Kris wishes to keep it in this forum that his choice. I am only the help. I thought however why I want to go off forum.
Ciao,
Adrian
911C4

PS: Regardless this forum will be kept up to date. For the record the 993 has the Bosch 5 PDAS/ABS system which only uses 3 sensors and a viscous coupling. 5% front and 95% rear being normal. The 964 is purely mechancial with a Bosch 2 PDAS/ABS system using four sensors and differential locking. The units and systems are not compatible and this is a big worry.

 

Thanks for the tip Mike. Have actualy explored that route and will hopefully track down a good mechanic soon.

Didn't expect to see this much interest in my problems but will be more then happy to post my off board discussions with Adrian here. What I'll do is cut and paste my stumbling and Adrians' advice here as we go along. Are there any limits on post lengths though? Can someone pls. advise?

Anyway here's my reply to Adrians' last post.....


Hi Adrian,

Many thanks for the all the advice so far. Have printed your last post
out ( Yes I do not have a good mechanic!) and will check in detail what
you have told me to over the weekend. Plus, all you have written has
given me a better understanding of how the 964 works which is a far cry
from when I first started, I ws literally 'flying blind'!

Note your conclusion that it's possible that the former owner was aware
of the problems with my car. His name is Peter Ng but I don't think that
info will be of much use as I don't believe he was ever on the Rennlist
forum (or any other for that matter!). She drives well and the engines
strong though so I want to try and fix her with a lot of help from you!

Kris

 

krish:

Since you don't have an owners manual, maybe you can find someone who has one on this list who owns an '89 model. Perhaps you could get them to scan the portions about the dash lights and how they work and then e-mail you the scans. I have a U.S. model 1991, so what my lights say and do will likely not match yours (they might), but maybe someone on this list has such a manual.

Just food for thought.

Good Luck,

Bill Wagner