I have not used my 964 C4 1992 for a few days, when i used it today after about 5 mins the Four Wheel Drive & ABS warning lights came on and stayed on. Allthough the lights where on there did not seem to be anything wrong with the car.a few miles later i stopped the car and re started the engin, this time thank goodness the lights went out and stayed out. can anyone tell me what they think the problem is? this is the 2nd time it has happened. Abit more background info the car is a targa and has not been garaged for a week or so and it has rained <img src="confused.gif" border="0">

 

How fast did you go....?

did the light come on just when the rear wing should have extended....?

Chech your wing is working with the switch beside the gear leaver first.

 

thank you irishdriver for your input. yes i would have gone fast enough for the wing to have gone up,and i will cheque that the wing is working. can you tell me though why the wing should effect the warning lights.
simon

 

Simon,

I think that when the ABS & Traction Control lights come on, it means that the system is not up to pressure. Did you get the brake pressure light too? Had you been driving the car aggressivly - ie. using a lot of hard braking in quick concession? Have you checked your brake fluid?

Try searching the archives for clues, but my guess would be either bad battery, bad alternator or lazy traction control unit. Although I could be wrong....

Hope this helps! Maybe Adrian will chime in and give his thoughts...

Andy

 

Thanks Andy I will take your advice, However i still think that the solution has yet to be found, I was not pushing the car too hard as i had only been going for a few mins. in fact on refection as the car got fuul warmed up (about 20 mins) the problem goes away.
thanks again
simon

 

Guys,
This is not an uncommon problem when the C4 has not been driven for a while or has been driven on lots of short trips. The first thing one does is go for a decent one or two hour drive.
If the problem persists then we check battery and alternator/regulator for correct operation and then we start troubleshooting the system.
The PDAS/ABS control unit in the C4 is VERY sensitive to low voltage situations.
Of the course the other issues are,
Air in system.
Age of brake fluid.
Brake fluid level.
Do you drive off with the brake warning and PDAS warning lights still illuminated.
Do you get the warn horn when the lights come "ON".
Ciao,
Adrian
911C4

PS: There is heaps on this subject in the archives. However do not start pulling things apart, purchasing new parts until all the troubleshooting steps have been carried out. 60% of these problmes are caused by basic electrical issues with the C4. LOW BATTERY!!! for whatever reason. Oh yes, after heavy rain this problem can also occur. Water in the connectors of the front wheel speed sensors.

 

Adrian, Thanks very much for your input I will cheq out all the things on your list.
And NO the horn dose not come on.
simon

 

Dear Simon,
This is very significant. This indicates a brake fluid level problem or a low battery. Seeing as it has been raining I would recommend the following.
Most obvious thing is check the brake fluid level.
Brake fluid tank is on the right hand side (looking from front) under the carpet mounted to the side bulkhead.
You must have engine running to check brake fluid level. Even better if you have the pump running.
Next is to check the connectors at the top of the tank. You will see they are spade connectors. After heavy rain it is quite possible that water has got past the seal, run down the hood/trunk lid and dripped into the carpet. go through the carpet and filled up the top of the brake fluid container. This then shorts out the connectors and bingo on come the lights, without horn. I am assuming the horn is functional and has not been disconnected. This happens as well.
So summary,
Check brake fluid contents and check for water contamination of the brake fluid sensor or the connectors.
Still check battery and alternator afterwards if problem not solved. One last note. If you are down on brake fluid you most likely have a leak unless you do track work and have boiled the fluid off. FIND the leak.
Ciao,
Adrian
911C4

 

Thanks again adrian will do all of the above and report back.

 

Dear Simon,
Look forward to hearing that you found the problem and solved it,
Ciao,
Adrian
911C4

 

I too have found that 964's are very sensitive to brake fluid levels. My warning lights come on when ever the level is below the top line. I top it off and problem is solved.

Rob

 

Dear Rob,
May I suggest you find out why you need to replace brake fluid. You have a C4 and you should not be using or losing brake fluid unless on the track. Check your hydraulic pump on the ABS hydraulic units for leaks. Even if you find the slightest evidence of fluid on or around the ABS hydraulic unit I recommend immediate action be taken to repair the problem.
Ciao,
Adrian
911C4

 

Dear Adrian,
AS luck would have it, or not wichever is your point of view the car has been booked in for a 6000 service some time before this problem arose. it is now in the shop and i have asked them to identify the problem. there current diognosis is that there is "a leak on a switch in the brake booster system" but they are yet to confim this. how dose this sound to you? the leak is not big but enough to have this effect, they also say that the the are a bit spongy, dose this sound right to you.(i would not know all these things as for me the car is a new experiance as up to now i have only had 911 3.2s.

 

Dear Simon,
This is the pressure switch and yes they do leak. This would certainly cause your problem. Regardless the leaking part must be replaced. There have been a number of failures of these pressure switches in recent weeks.
Ciao,
Adrian
911C4

 

Adrian, iwent to see the car this aternoon, and can confirm the pressure swich is leaking. looks as if the problem is sorted .
thanks again for all your help
simon