jjrichar

Thanks for the response. Much appreciated.

Sorry for the nagging questions but learning about failure modes is something I'm really interested in.

It seems very unlikely (clearly not impossible) you would get two entirely separate sensors fail in the one transmission. Did it look like a common problem, maybe wiring or the plug, that may have caused both to fail? Were the failed sensors bench tested for individual response once separated. This may not have been done but I thought I'd ask anyway.

Also, have you ever had any issues with speed sensor response once fitted? Every one I've fitted has been plug and play without issue, which is pretty normal for any other type of speed sensor.

Thanks again

wjk_glynn

Ditto here as well.

I'd been assuming if you saw PDK temperature errors, it'd be most likely due to a bad crimp: https://rennlist.com/forums/997-foru...procedure.html

Any ideas on how a bad speed sensor manifests as a temperature error?

And any particular temp error code pattern?

Thanks.

Karl.

PV997

The concern I have with all this is that there's around 100k out-of-warranty PDK 911/Cayman/Boxsters in North America with only a handful of known speed sensor failures. It's not perfect of course, but that's a very low failure rate by any definition. There is no limited-life wear-out mechanism (like a bearing as an example) that would cause eventual failure. The reason we are even talking about it is because Porsche won't sell you a replacement in the unlikely event it fails.

Add to that there is no mechanism that I can imagine which would cause both to fail, they are decoupled and failure of one does not make the other any more likely to fail. In fact, the odds of both independently failing on the same transmission would be astronomical (since compound failure rates are multiplicative). Plus we have no reason to think that the T-Design speed sensor is any more reliable than the factory sensor. Maybe we will some day, but we don't now. Preventative replacement just doesn't make sense IMO (same with the distance sensor).

I'm glad we now have a replacement option and shops are certainly entitled to do what they think is in the customer's best interest. But this seems like it needs more thought before it becomes a routine practice, particularly since the new speed sensor is very expensive. If it was a couple of percent increase in the total job cost then I get it, but it's more like a 20+% increase.

Noah Fect

Until someone can come up with a failed speed sensor for RC analysis, it does seem speculative to replace them "while you're in there."

PV997

Yup, I do RCCA for a living which is why I think this needs more thought. Don't get me wrong, I don't want to imply I'm telling shops their business as that's not my business, they need to do what's best for their customers. My concern is that this becomes a general industry "best practice" without due diligence.

wjk_glynn

Hi ​​​​@notfastenough, super curious to know more.

Can you share a bit more?

Any particular pattern to the temperature errors preceding the speed sensor failure?

Thanks.

Karl.

notfastenough

2013 981 is one of the first we saw with a speed sensor issue. After a long drive it went into limp mode accompanied by distance sensor codes and P0732 and P17F1 over temp codes. Harness crimps were checked and confirmed to be ok. Since we had the opportunity and time to do some testing we installed a T-Design distance sensor, cleaned the speed sensor, tidied up, and reassembled. Fresh fluids and a healthy test drive and we were right back to limp mode and the same over temp codes. Only after a speed sensor replacement was the car fixed. And yes: speed sensors are plug-n-play.

I can understand DIY'ers may be willing to take a chance, but legit shops would be foolish not to replace both sensors while in there. Even with a very low failure rate I refuse to put ourselves into a situation where an out-of-state owner has a breakdown because we cheaped out.

wjk_glynn

Thanks.

byroncheung

@notfastenough i'm going to replace my distance sensor soon i'm thinking if i should get the speed sensor replaced while in there. to get a sense of how common the speed sensor problem is relative to the distance sensor problem - how many distance sensors you guys have done in the last 6 months (v.s. 4 speed sensors)?

toddlamb

Just got a car in that needed a speed sensor - it's not a common issue but it is a real thing.

notfastenough

Suffice to say we've replaced a buttload of distance sensors so it's a low percentage of failures on speed sensors.
Byron, I'm going to offer some free advice (again). Four months ago I believe both Todd Lamb and I advised you that your problem was the distance sensor. You've been kicking against the goads ever since. Don't make the same mistake again; suck it up and replace the speed sensor!

You're welcome.

wjk_glynn

Hi Todd,

What kind of symptoms/codes did it exhibit?

Thanks.

Karl.

REvans89

Hi gents,Does anyone please have the sizes for the threads at the rear of the gearbox. The upper thread is slightly larger than the lower and I can’t for the life of me on any of the walk-throughs find what thread sizes they are. Any information or direction on where I might find them greatly appreciated

byroncheung

I appreciate your advice. I did agree with you from the beginning that the problem is most likely the distance sensor, but hey, when we found out it worked again after a recalibration, as a computer geek, I have to play around with that to see if I can find a pattern there! Don't worry though, the distance sensor will get replaced soon, and again thanks for your input.

As for the speed sensor, I think I will roll my dice, doesn't seem to be as common of a problem compared to the distance sensor, and I'm willing to take my chance here to save a thousand dollars.

Again, thanks for your time, input, and contribution, not just to my particular problem but to this whole PDK failure scene in general.

saabin

Is that what it costs? Or are you just guesstimating? A grand incremental costs on top of the other work? Sounds like a lot.