Aaargh - PRNDS!

[David's8]

Originally Posted by HPsauce

Thinking back to that comment, now you've had yours out and found only wear (similar to mine?) maybe this needs to be viewed as a "consumable" replaced maybe on a similar cycle to the cam belt?

Looking at mine carefully I could see a bit of "clumping" of the lubricant/grease so do wonder if it's just a combination of wear, debris etc. making it less reliable as it ages. The sliding contact design doesn't really seem to be engineered for tens of thousands of operations, after all it moves presumably every time there's a gear change, maybe with changes in torque converter slip as well?

I think you might be right in that it seems to be a known failure item at around 100k. Do we have any data collected on when these have failed on forum members cars? If none, then perhaps we could ask. For info my mileage was at 109,700.

[MikkiJayne]

Originally Posted by HPsauce

So how, if at all, is it involved if I change gear with the thumb buttons on my steering wheel?

Its not really. As long as the TCU detects D or S it'll allow program override by the buttons. Same as shifting with the lever in D - the F125 doesn't actually move at all when you push the shifter over in to +-. Thats all done in software.

Mine is at 114K.

[HPsauce]

I'm at 97,000 miles but it's been misbehaving for ages.
That said, I do happen to know that a previous long-term owner did a lot of short journeys.

[HPsauce]

Originally Posted by MikkiJayne

It does - its directly attached to the gear linkage.

Knowing little or nothing about how these gearboxes work and are controlled I'm nonetheless a bit surprised by that.
I had assumed it was taking physical information about the state of the gearbox and relaying that electrically to the TCU.

If it's just the physical position of the gear selector lever, why not detect that in the cabin? Or is it to eliminate the possibility of a loose/worn mechanical link (cable?) and get the information "from the horses mouth" so to speak, i.e. as close to the gearbox as possible.

Or is there a belt and braces approach, with sensors on the lever as well? There obviously are for the tiptronic elements.

[MikkiJayne]

Originally Posted by HPsauce

Knowing little or nothing about how these gearboxes work and are controlled I'm nonetheless a bit surprised by that.
I had assumed it was taking physical information about the state of the gearbox and relaying that electrically to the TCU.

If it's just the physical position of the gear selector lever, why not detect that in the cabin? Or is it to eliminate the possibility of a loose/worn mechanical link (cable?) and get the information "from the horses mouth" so to speak, i.e. as close to the gearbox as possible.

Or is there a belt and braces approach, with sensors on the lever as well? There obviously are for the tiptronic elements.

The tiptronic switches are on the gear selector, but the F125 does everything else. I can't see any reason why it couldn't be in the selector tbh.

The F125 tells the TCU which gear is selected, and the shift lever also has mechanical functions inside such as engaging the parking lock and interacting with the valve block. The cause of PRNDS in this case is the TCU not getting sensible signals from the F125, rather than any feedback from gubbins inside the gearbox (like the speed sensors etc).

[Adrian E]

Mine was done at about 42k and 9 years old!

I didn't leave mine faulty for long and just replaced it rather than attempting to fix it

[HPsauce]

Originally Posted by MikkiJayne

The switch is reassembled now

How did you fix it back together, riveted again or small bolts/nuts?

[MikkiJayne]

I had some M4 button head screws and nylocs which were just the right size

[oldnick]

Originally Posted by David's8

I think you might be right in that it seems to be a known failure item at around 100k. Do we have any data collected on when these have failed on forum members cars? If none, then perhaps we could ask. For info my mileage was at 109,700.

same mileage for me ; have got the 8 pin not the 9 pin; only done a few thousand since cleaning up the connector but not a trace of a problem since

my current theory is that there is a combination of problems that causes the clean up to fix the problem ie a poor contact on the connector reduces the signal strength to the internal contacts which , being worn , need the stronger signal
had already planned the bolt + nylock reseal as per MJ if it comes to it later
no lift available but still have my motorhome ramps so will try running the front up on that then blocking the side

[David's8]

Originally Posted by oldnick

same mileage for me ; have got the 8 pin not the 9 pin; only done a few thousand since cleaning up the connector but not a trace of a problem since

my current theory is that there is a combination of problems that causes the clean up to fix the problem ie a poor contact on the connector reduces the signal strength to the internal contacts which , being worn , need the stronger signal
had already planned the bolt + nylock reseal as per MJ if it comes to it later
no lift available but still have my motorhome ramps so will try running the front up on that then blocking the side

You may well be right there about poor connections.
I hope that the ramp option gives you enough room. If there is any degree of extra force needed for stuck bolts/exhaust movement then you may need a lift. MJ is just across the channel and has a queue of '8s waiting!