DavidI

Hi Folks,

I wonder if I can pick your brains:

Last week I spent way too many hours stuck in town at crawling speeds. I noticed the steering wheel seemed very slightly off-centre when driving straight, but it was so slight I was questioning whether it might be the camber of the roads.

The next day on a normal blat between office and home the ABS and PDAS lights came on (with the warning !) and they now come on without fail about 30seconds after starting up and driving off. I'm also now convinced that the car is pulling ever so gently to the left, more obvious (but still only slight) under braking.

I've picked up the excellent lists for causes of the warning lights from the search facility and have so far just checked the brake fluid level, which is right at the top, and the tyre pressures which were fine.

Has anyone experienced a suspension problem that causes the ABS to believe one corner or one axle is out of kilter (as if the rolling radii were out by more than their allotted 6.5% or so) which then takes the PDAS offline?

I know the wishbone bushes at the front were past their best, though the front end actually seems fairly sharp and I would expect it to feel worse than the very slight pull I am feeling. Perhaps a front diff issue could cause both the pull and the lights?

Any feedback gratefully received. I would sooner get the car to the shop pointing them in the right direction than let them check the usual accelerometers, ABS sensors etc. if I'm right thinking the steering play is too much of a coincidence.

Many thanks,
David

Rocket Rob

Does the car pull to one side when under power and when under braking, or just one of these cases? I'm wondering if you might have a sticky brake pad or caliper. If you jack up the car, do each of the wheels spin freely?

Another thought. How old are your tires (tyres)? I have see tires go bad (separated internal belt) that caused a car to pull to one side. Do you have access another set of tires/wheels?

DavidI

Hi Rob,

The car definitely pulls under braking and has what I would describe as more of a 'desire' to go left under power - hands off the wheel it will go left, hands on and it's more subtle, but yes, under power and under braking.

Tire idea is a possibility. I've a spare set of rims but they're tire-less at the moment. If the tires were at fault I'm then looking at a separate cause for the warning lights

cabjorn

Hi David,

I have experienced the same problem with the warning lights and also read about it in "Enthusiast's Companion"(witch i can recommend). The problem could appear if you have a bad battery or low voltage supply.

For problem with pulling, check wheel alignment.

altarchsa

Wheel speed sensors? Logitudinal and latitudinal sensors? The C4 has a pretty complex computer controlled system that transfers the power to the various wheels based on the signals from the sensors. Seems like your symptoms would be connected rather than separate issues (battery and brake pads?????).

I have not experienced it, but I've read posts from C4 owners who have experienced some unusual responses from the drive system to various road conditions, like the car shooting to one side or the other when both wheels on one side get caught up on a line of jiggle bars on the side of the road.

roadsleeper

The "Sputnik I" AWD system and the ABS system in the 964 C4s are pretty rudimentary, so I don't think a suspension issue would cause the ABS and PDAS warning/lights to be triggered. In my experience, this is more indicative of either the brake booster pump and/or the brake pressure accumulator being on their last legs... Have you noticed any change in the brake pedal feel or braking in general lately?

altarchsa

Go by (or buy, if you don't have it) the book. Streather's Porsche Companion has a very detailed explanation and troubleshooting process fro this issue. I've experienced it myself and it can be a very frustrating thing to resolve. For example, in my case, new plug wires and coils straightened it out! That's why I wouldn't suggest a single most likely issue. However, as previously stated, the symptoms are indicative of low hydraulic pressure... or wheel speed sensors.... or low fluid ......or......, uh, use the book.

DavidI

Thanks all. I'll get the car booked in and let them hook it up the hammer. It's so subjective, but one day last week no lights came on and the pull seemed to have abated too. The battery and earth lead were changed recently, so I'd expect voltage to be OK, and I've not noticed any change with the brakes. Let's see if the hammer can pick up on anything.

Henry964

These lights issues are very difficult to solve, I´ve changed nearly everything electrical in my C2 (wires, plugs,battery, rotors, caps etc) and I still get them from time to time,but only in the highway and only if I have a passenger, if I am driving alone no christmas tree at all, I think maybe it is something related to the right seat touching something....go figure

darth

Try driving on the opposite side of the road where you experience the issue and report back your findings. It may be the crown (i.e. camber) of the road.

Bill