Patrick L

Hi,

I'm new to this board, and I'm currently looking for a 964.

I found a '90 C4 last week, everything looks pretty good, except the ABS/4WD warning light. I read some articles on the web, but seems the symptom is different.
What happened is as follow:

At start, the red 4WD light is on and stay on. When you press the brake during drive, ABS light will on, and then stay on.

Also, when you turn the 4WD switch on the first time at start, the green 4WD light will blink, but whe you tunr it 3 or 4 times. it just won't light up anymore. But you can always hear something under the floor is moving when you turn on or off the switch.

The owner said it's only the ABS control unit problem, but I'm concerning if there is any other parts are damaged.

Anyone know what happened? If it's only the control unit, that will be the easy one, but if some other systems are in trouble, I'll certainly re-consider this car.

Thanks!

Patrick

Andy Roe

Not sure what it is, but if it's the ABS control unit, I'd say walk away! It's an expensive part to fix.

Adrian

Dear Patrick,
First of all the C4 is an AWD. The green light is not the 4WD light it is the traction control activation light. Either automatic or manual activation. This should not work. Porsche disconnected them at the factory. This means the current owner or a previous owner has done some DIY wiring. There is no such thing as a 4WD switch. What you are referring to is the traction control program switch. If the traction control system has failed and the red warn is on then this system will not work either.
From your description I do not think it is the control unit. I think it is a traction control system component failure or a brake boost hydraulic problem. The PDAS (traction control warn light) activated on its own tells me immediately that the problem is related to pressure or the slave cylinders and not the control unit. The fact that the ABS light is coming on is actually telling me the control unit is okay. You comments on the noise underneath also suggest my diagnosis is correct. You can read about this system in the technical section of <a href="https://rennlist.com." target="_blank">www.rennlist.com.</a>
I would not purchase this C4 unless you can get the price discounted. Fixing the problem will be quite expensive but not out of this world. It is the DIY work which worries me.
Ciao,
Adrian
911C4

Patrick L

Adrian,

I read lots of your articles and that's very helpful!
In one of your article you mentioned a "yellow led" that will indicate PDAS. Where is it? Is it on the meter face? Also, when Porsche de-activated greed PDAS light, is the light still on meter face, just won't function?
For the noise coming from underneath when turning the PDAS ****, what's the problem? Central differential lock?
Thanks!

Patrick

Patrick L

BTW, how much $$ should I expect to have this problem fix?

Patrick

Adrian

Dear Patrick,
The yellow LED is above and to the right of the traction control program activation **** on the centre console. By the little diagram there which shows the rear differential. The LED only illuminates when traction control program is activated or the rear diff lock activates in normal automatic mode. It does not activate with the centre diff lock.
The noise coming from underneath suggests the centre differential lock system has failed. If the slave cylinder has failed the cost of repair is not so high. Maybe $US300 but if the differential lock has failed you will have to drop the engine and transmission and repair it. This will take you towards $US1500 plus. In Taiwan of course I do not know your prices.
Porsche de-activated the green light because it was deemed a distraction for driving at night and that a flashing light in a warn cluster and this is not a warn light may create angst for the driver.
If you look at all the instruments you will see a complete range of lamps many of which are not used in a particular model. Porsche did try and standardise the instruments.
Ciao,
Adrian
911C4

Carl Muckenhirn

I've recently inherited a ghost as well.

I just had the suspension re-done (H&R "super sport") and put on my summer tires. While in the shop they were supposed to also re-do the brakes (new rotors and pads), but didn't so I'm going back this week.

Now for the problem. At random intervals (no fixed pattern) both the ABS and Interlock indicators will light, with the system warning horn sounding as well. I've caught it a couple of time out of the corner of my eye and the lights come on simultaneously.

Interestingly, the interlock system is functioning (at least the led next to the locking switch flashes at appropriate times (rough road)) after the interlock warning light illuminates.

Haven't been able to discern if the ABS is still active or not. (Too dry, or too much traffic!)

Any ideas? Its going back to the shop so hopefully they'll figure it out, but I like to be prepared for the story...

carl.