OT: help with traction control problem

[sawood12]

I've got an issue with TC on the SMax and anticipating the usual un-helpful response i'll get when I take the car into the dealer to look it over - i've already had the usual "We've hooked it unto the diagnostics computer and it came up with no fault codes so we can't do anything else" at my last service when I asked them to look into it. I'm taking the car back to them as things seem to have got worse and I want to approach them with some semi-educated ideas as to what may be causing the issues as it is just getting silly now.

Previously the TC on the car hardly ever cut in, even when I was driving the car in a 'spirited fashion', and it only cut in at expected times - i.e. when pulling out of a junction quickly or when on snow and ice. There are a number of corners around me that you can take at high speed, where the TC now cuts in a good 15mph earlier than I could take the corner previously without the TC cutting in.

It could very well be that the TC system itself is working fine and something else is kidding it into thinking that something is wrong.

This all started to happen after I replaced the rear tyres so my first suspicions lie with something to do with the rear tyres. They are the same brand and correct size as the older tyres. At first I thought that maybe they were slightly slippy due to releasing agent or something on the surface of the tyre, but this should have scrubbed off by now.

I'm wondering if something else may be triggering it for example a worn bush or something that may be causing an effect that I can't detect, but the TC system can? Has anyone got any experience of mis-behaving TC systems on other cars? I know it is a long shot.

Thanks.

 

[Riverside]

TC works by comparing the speed differential of the wheels. Changing all four tyres at the same time is probably recommended in the manual.

 

[sawood12]

I thought that at first, but I have changed the front tyres before as the wear rate up front is about twice that of the rear and I had no TC issues. I'm not a fan of tyre rotation as you only end up having to replace all four tyres instead of a pair at a time. I might swap the fronts with the rears to see if that has any affect. The only difference this time is that the tyres are different, though they are the same brand and thought to be equivalent to the ones I replaced but with a different tread pattern. I hope it is not the case I need to replace all four tyres as they are F'ing expensive due to the weight rating.

Given the speeds at which the TC is now kicking in - i.e. well within the handling and grip capabilities of the car, the issue can't be due to any of the wheels getting anywhere near the limits of grip so i'm wondering if modern TC systems not only monitor and compare wheel speeds, but also monitor the movement of the car with accelerometers i.e. body roll. I know that the braking system uses accelerometers to vary front/rear and left/right brake bias as you're braking to prevent any wheels locking up during heavy braking and unloading any axel or corner (this car is better on the brakes than my 944 ever was despite it being nearly 2000kg's). It could be that maybe an ARB bush is wearing and the body rolling around more than usual which may be kicking it in? I've not noticed anything from the seat of my pants, but if it is a slow wear mechanism I might be getting used to it as it is deteriorating and not noticing.

Oh, well, i've done some Googling and I've not come up with any generic well known issue with TC systems so i'm into the area of trial and error and hoping the dealership can find something.

 

[Riverside]

I agree you're going to have to just see how it goes, it's possible that the learning system needs more time to adapt to the change in tyre diameter, or that the logic expects either new tyres to be put on the front (I appreciate general advice currently favours putting new tyres on the rear) or more likely, it expects all four tyres to be changed at once. If there is a rule like this in the ECU I'd expect it to be in the car's handbook (and probably advises changing all four tyres).

If it was a car I was prepared to invest a bit of spit & polish on, I'd try swapping front & rear tyres, & if the problem went away consider renewing the (now rear) tyres.

On that type of car I'd be inclined to either drive within the problem or just switch the TC off.

 

[VanhireBoys]

I am no expert but a friends 09 Mondy had an intermittent problem with the ABS/TC. No code showed up. He took his time and checked the 4 pickup sensors and found one of them dodgey... ! Replaced it and no further bother ! Check the wheel speed sensors first!
They could even be dirty or have a damaged cable.

As said above the system for ABS/TC works by comparing the rotational speeds of each wheel.

07 Mondy had the ABS control unit fail ... It is located under the cup holder. It fried because the fella used to leave his mobile in the cup holder. Ford had an upgraded ABS control unit from 08 on due to this issue....

I will ask Stephen who works for Ford and see what he says []

 

[944s2]

Would not have thought T/C worked with rear wheels only

The fronts only by measuring rotation difference between them( I could be wrong though)

though they are the same brand and thought to be equivalent to the ones I replaced but with a different tread pattern.

Is it possible just wear on front tyres or different (Harder compound) tyre therefore less grippy?

What were two tyre types

 

[944Turbo]

Is it traction or stability control? on my Audi they both use the same dash light.
Tony

 

[sawood12]

ORIGINAL: VanhireBoys


I am no expert but a friends 09 Mondy had an intermittent problem with the ABS/TC. No code showed up. He took his time and checked the 4 pickup sensors and found one of them dodgey... ! Replaced it and no further bother ! Check the wheel speed sensors first!
They could even be dirty or have a damaged cable.

As said above the system for ABS/TC works by comparing the rotational speeds of each wheel.

07 Mondy had the ABS control unit fail ... It is located under the cup holder. It fried because the fella used to leave his mobile in the cup holder. Ford had an upgraded ABS control unit from 08 on due to this issue....

I will ask Stephen who works for Ford and see what he says []

Thanks, this could be a similar thing as i've only been having the problem following the rear tyre replacement so it is conceivable that the tyre fitter inadvertently disturbed something when he was removing/refitting wheels. I'll request they check each sensor individually.

I'm not convinced that it is the difference in tyre diameter between worn and new tyres as i've had the fronts replaced before with no problems whatsoever.

Good point on TC vs stability control, i'm not sure what i've got. Either way whatever it is there must be a fault as there is no way i'm loosing traction on any corner at the speeds it cuts in. The tyres on the car were Goodyear Excellence, and I replaced the rears with Goodyear Efficient Grip. The Excellence tyres were difficult to find and the equivalent tyre in the Kwik Fit database was the Efficient Grip and explained as an equivalent tyre but with a different tread pattern. Given the difficulty in my being able to find the Excellence tyre, even at the dealership, maybe this is the replacement tyre.

Anyway, thanks for your input guys, as always even when faced with a topic that is a bit obscure and even non-Porsche related i've got a wealth of sensible suggestions and plenty of food for thought.