I have a 1990, 964 C4 Cabriolet. Since I bought the car about 6 months ago a red light showing the 4 wheel drive sistem is always on.

I read in the manual that you may used the center dash control to lock the transmission differential for low speed traction. I try moving the swicht to see if the light turns off but it did not.

I am wondering if this is normal, does it mean that the differential is lock and therefore their is a problem or worse it could cause some mayor damage to the car.

please give me some light into this problem.Incidentally, I change all the fluids in the differential and transmision and it look fine.

 

Are you talking about the red light on the dash or the orange light just above the diff. lock switch on the console? The orange light is what comes on when the diff is locked or the system is activating, the red light on the dash is an error indicator. If the red light is always on then there is a problem with the diff system. Is the ABS light on the dash also always on?

 

Yes, is the red light on the dash, yes the ABS is also on. is it related.....

 

Yes, these lights often come on together. I had the same signs on my car and it turned out to be a bad pressure accumulator valve for the hydraulic system. Although the car seems to behave normally not maintaining adequate pressure in that system can be dangerous. I would get it looked at quickly.

 

This also happened to me in the past on two occassions, first time it was brake fluid level that was just a bit low (topped it up, and the warning lights dissappeared), second time it was the abs sensors failing (had to replace them)...

Harold

<a href="http://members.rennlist.com/complete964" target="_blank">Complete 964</a>

 

O.K. I think I will have it check by the dealer with a Bosh Hammer since all of this happend after a brake job I did to the car just after I bought it. all the lines where bled but you never know.

Anyway thanks everyone.

Gerard

 

Now that Harold mentions it, after my car had been repaired the same thing happened again but it was just low on fluid. The dealer did not properly refill the car after replacing the valve. Since you just changed fluid you may want to make sure that the resevoir is topped off, maybe you were low before and still are after the service.

 

Guys,
Please check out the archives and the technical section of rennlist. There is a huge amount of data. The lights coming on after brake work is very common. A C4 needs to be done in accordance with the maintenance manual instructions. There are heaps of threads about this. It is just costing you uneccesary money, time and frustration if you do not bleed your brakes IAW the book.
The PDAS and ABS RED WARN LIGHTS tell you that traction control (not AWD) and the ABS system are not available and you need to correct your driving accordingly. The AWD system is 100% mechanical. The AWD in the C4 is always in AWD mode. 39% front and 69% rear. This only changes with torque transfer via the traction control system. Very quickly and very temporarily by the way. There is no AWD warn light.
Ciao,
Adrian
911C4

 

That would be 31-69, right?

 

Yep, typing too fast, post edited,
Ciao,
Adrian
911C4

 

well, I can see on my dashboard a red light on, with a small diagram of the 4 wheel drive sistem. You are saying that this light is telling me that I have no traction control and has nothing to do with something not working properly in the 4 wheel drive system?....

thanks for the help, and forgive my novice questions.

 

Dear Gerard,
That is exactly what I am telling you. The picture actually indicates thelocation of the 2 differential locks which are affected by the lack of brake pressure or whatever else is causing the problem.
PDAS and ABS lights on indicates a traction control or abs problem.
PDAS and Brake warn lights on together indicates a brake fluid or brake pressure problem.
PDAS-ABS-Brake Pressure and Yellow Led (by **** on centre console which only shows the rear diff lock) all on indicates a lack of electrical power available.
AWD problems are indicated by horrible grinding noises, the squeal of metal turning into shavings and a gradual slowing down of the C4 until it refuses to move anymore or go around corners,
Ciao,
Adrian
911C4

PS: I forgot to answer part of your question. Basically the PDAS and ABS system failure cannot harm your C4 directly. There is one problem though that can. If a diff lock is leaking fluid it tends to leak it into the transmission. This is not good. However you will see the brake fluid level drop so this should be totally obvious. The traction control program (fancy gimmick really) will "never" work whilst the PDAS light is on. It works from standstill to 40kph only anyway and you need to careful when you engage it because you will have "Massive" understeer. This program is designed to pull you out of deep sand or snow only. It has no other use apart from Adrian using it for troubleshooting.

 

Adrian -- is Rick's guess of acculumator failure accurate? I had what apeared to be this set of errors last year, and after accumulator replacement, coupled with full Hammer-drive sytem bleed, have not seen that light since.

Was it the Hammer bleed that saved the bacon, or the new accumulator?
1989 K series C4.
C

 

Adrian,

Thank you very much for the help. I understand now. I actually call the porsche dealer here in Panama about having my car check with the bosh Hammer. They told me that they do have a Hammer but since they are a dealer since 1999 they actually don´t know how to used it for a C4. They also told me that they did have the program for the Hammer for the 964 series. Any ideas on how to do a diagnostic and most importantly turn off this lights.

Also from your message I am assuming that if everything is fine and the ABS and PDA ligth just need to be reset by the Hammer i should be fine (I check the fluid level and did the brake pressure exercise and I am not hearing any grinding sound, everything was O.K.). Basically in theory I could drive the car and I am not really doing any damage to the car.

Regards,

Gerardo

 

Dear Gerado,
I will answer your question first. If just the PDAS and ABS warn lights are on and not the brake warn light as well you are not doing anything to damage the car. The fact that they are on before you drive off tells me that you are looking at electrical or control unit failure. The system has been inhibited. Lights coming on whilst you are driving requires a tad more care.
Dear Craig,
The system bleed often cures many problems. Especially if you have the brake warn light on as well. Accumulator leaks which do happen, they age and the pre-charge leaks down will cause pressure problems which will normally first turn on the PDAS warn and then the ABS as well.
I small point. The Bosch Hammer can be used to clear the fault codes. I recommend that this is done first and the Hammer left hooked up when you start again. This will hopefully show a fault code sequence. Experience in using the hammer is critical to avoid expensive purchases which do not need to be made.
I also recommend that you check all the options that are installed in the 964 and check that all relays and fuses are intact. I have discovered that playing with the drivers seat can lead to frying the control unit. This happened in Malaysia.
Unfortunately PDAS/ABS problems often take time to solve. It is a very complicated and interlocked system. One step at a time and accurate reporting of the fault lights illuminated is critical.
Ciao,
Adrian
911C4