Hi,
I recently bought a C4 964 and the diff warning light comes on, from time to time on the motorway, even at 70mph.

You get the usual beep, press the acknowledge button and then when the car is switched off and on again later the light is off. I had the big service a week ago and they said the computer log did not register any issues, so it may be a faulty/loose sensor.

Does anyone have a view on this issue, or has it happened to them or someone they know?

Advice always appreciated.

Thks.
D

 

Hi D,
bad to hear even the big service was just one week ago. Check the level of break fluid. It should be near the max. level. If this is ok check or let check the "pre-resistor" of the AWD. It's just a PCB with a resistor, a coil and a bi-metal switch. Clean the contacts or renew it. Cost can be approx 100 $ at Porsche dealer.

 

thanks, i informed the guys at the service centre, they said not to worry as nothing flagged in the computer log...I assume I can keep on trucking ? Or do you recommend getting it sorted ? thks

 

Dan,

This problem can so often be caused by high tension leakage through worn or corroded distributor caps and/or coils. Don't go spending money on misc. sensors or lots of labour time without checking the caps/rotors and coils first. I spend more than a year wasting money before I found the problem.

Regards

Dave

 

Had pretty much exactly this happening to me today for the first time. Also restarted the engine, and then it came back after a couple of minutes again while driving.



How can that have something to do with the distributor cap?
2 weeks ago I had both distributer caps and wires replaced at the workshop.

 

I'll grant you that the link isn't obvious but the reality is that HT voltage leakage from faulty or damaged HT cables and/or distributror cap allows high voltage current to pass into the chassis - and from there it disrupts the signals from the accelerometers to such a degree that the PDAS controller THINKS there is a problem when there very obviously isn't.

As I mentioned above, I spent more than a year getting wheel sensors checked and changed and a multitude of other things but changing the distributor caps and both coils finally nailed the problem that had been plaguing me every few miles. The problem never occurred again over a 3 year period.

 

Had exactly this with mine and eventually found an issue with arcing at the coils replaced and no issue since.

 

I tried pushing all coils today before driving home from work, and funny enough no issues on the 30 min drive home.
Fingers crossed

But when looking in that area I noticed that a wire/hose was not attached, but I can't see where it is suppose to go:

 

^^^ It is the distributor vent hose as seen here

 

This forum, freaking awesome!
I noticed the plug is very so I probably need a new one.

What is the function if the hose/plug?

 

The purpose of the vent is to push air into the distributor assembly to remove the ozone which, if left around the belt, will cause its failure and an expensive repair bill.

 

Dammit, was hoping it would give me 50 hp extra, but ahh well

Thank you for replying.

 

Nope, that's what stickers are for.

 

Do the warning and beeps coincide with going over a bump?

I had this intermittently too. This winter I switched the locks on before climbing the steep hill on my street that was a bit snowy. I was surprised that it didn't do such a great job at climbing the hill. Parked in the garage and noticed a big pool of hydraulic fluid under the transverse diff lock (the one at the bottom of the trans) the next day.

I think that the warnings were coming on because the leaky lock was losing hydraulic pressure. So anytime that the pdas engaged the leaky lock, the warning came up. It would sometimes happen over potholes, rough pavement, and highway bumps. Basically, if the pdas sensed that one wheel was spinning at a different rate and decided to enage the transverse lock. I noticed it happened more in cold weather.

We'll see if it happens again now that I've rebuilt the lock with new seals (thanks Colin at 9M!). You could engage your locks and drive a bit and see if you've got an noticeable drips.

Other possibilities are simply low fluid level. I'm not sure if bad grounds for the wheel speed sensors would do it? The wire terminal on one of mine was practically severed but soldering a new terminal didn't change the behavior. The grounds are ring terminals around an allen bolt in the front wheel carriers- from what I remember. They're definitely in a harsh environment.

 

No, it just happened during 30-50 mph driving straight.