ZedZed

I suspect they are all 'cheap TPMS' units, but Porsche charge a lot for them. I'd be surprised if they are not all made in China. Even the internal units only take a minute or two to fit - the snag is you have to remove the tyre. The external units on our Cayman have been 100% reliable over the few months they have been installed. The add-on box connected via USB (which then connects wirelessly with the TPMS unit, so no BT involved) is easy to set up too. I have hidden mine behind the HU. I think they are a good addition for the small outlay.

ZedZed

Agreed. And if he uses Carplay or Android Auto, the GPS comes from the phone anyway, not from the car antenna, so that won't make any difference to him. As you say, if he wants to use the inbuilt GPS, then the supplied antenna works just fine. I installed a HU in my Lexus and used the supplied GPS antenna and it worked perfectly. I hid the antenna behind the HU, stuck to the underside of the dash.

ZedZed

Thanks for the feedback. Glad you got it sorted.

drawz

CarPlay and I assume Android Auto can use the GPS data from the head unit, which is great because cars with factory GPS have a nice big antenna on the roof (or other good location outside the cockpit). It also helps preserve your phone’s battery life while navigating.

This is a random link, but if you google, you will see similar responses else where.
https://discussions.apple.com/thread/255275683

ZedZed

I don't see how that is possible. The navigation app when using CP or AA is running on the phone, not on the HU. So I don't see how an app running on a phone can be using GPS from someplace else. I guess an easy way to test it is to turn off GPS on the phone and then see if Waze etc still works. Obviously, if I turn off GPS on my phone and then try to use Waze, it doesn't work. I just verified that (although it's pretty obvious). Projecting that copy of Waze to an external device, which is what AA and CP do, doesn't seem, to me, to then be able to use the HU GPS. I am prepared to be proved wrong, of course, if someone can explain how it could work.

bigkraig

7870 discovery will have to wait, chstek said they were sold out and recommended i cancel and order a 7862

ZedZed

You'll get more hands-on support here for the 7862.

bmxtreme

Removing the tires is the main reason I wouldn't consider the internal version. I am not sure how many actually mount their tires, but it cost approx $125+ to have a shop here dismount/remount, which is enough to buy a set of OEM TPMS.
Many stuff I got from AliExpress have been questionable in quality unfortunately. I guess until I hear someone that says their AliExpress TPMS lasted them at least 5yrs, I probably won't count on them being the same. I recently swap out my factory TPMS which has been in the car for 10yrs and still working.

drawz

This is from Apple’s WWDC 2016 conference video transcript. The requirements may have changed since 2016, but doubt they would go backwards and not require it. The data is sent via the Carlink or ZLink app back to the phone, just as it is with microphone, button, or touchscreen inputs.

https://developer.apple.com/videos/play/wwdc2016/722

An alternate test would be to unplug your head unit GPS antenna and see what happens. This also sounds like it could vary depending on wired vs wireless CarPlay (I’ve only been using wireless). Zlink vs Carlink or specific navigation apps are also potential variables between our systems.

andy2111

If it helps I have been running Chinese add on TPMS on my Land Rover Defender for 3.5 years and apart from replacing the batteries they have proven to be reliable so far..

ZedZed

Yes, removing the tyres is a PITA. The external TPMS are a great solution IMO. They genuinely are hard to spot if you don't already know they are there. TPMS sensors don't normally 'fail' as such - what happens is their batteries eventually expire. I've had TPMSS batteries 10 years old and still going strong. The internal type don't have replaceable batteries, so once the batteries die, the unit needs replacing. The external units have replaceable batteries. I;d recommend external, but it's a matter of individual choice.

ZedZed

Thanks. Next time I am in the car I will switch off GPS on my phone and try it out. I'll report back.

So, is the car antenna/GPS always used? I won't be routinely turning off location services in my phone as I need that for all sorts of things, but it is an interesting subject (for me at least).

EDIT: that info from Apple implies that not all cars have the ability to send the data back to the phone. I wonder if our HUs do? I'll find out when I try it out, I guess.

drawz

I think if you turn off location services on the phone side, that would disable any location data regardless of source (including from the head unit). It appears to work for me though and Apple suggests it’s required for wireless CarPlay. Of course, these are sort of unofficial devices that may or may not follow all the rules.

bmxtreme

That is the problem - battery replacement. If the internal TPMS runs out of battery, you need to dismount your tires to get to it.

andy2111

I'm running the external tpms sensors and you just unscrew the cap to swap the battery. Takes 2 minutes.