How-to: Disconnect 12v battery

[Dee]

Always use at least TWO 10mm sockets as they usually don't hit the floor when you drop them into your Taycan.
I'm sure everyone knows that but just a heads-up.

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[Porsche-Guru]

Thanks to W1NGE for posting this.
It has sorted out my app issues and all seems to be working fine now.

The only thing I would say is that removing the negative terminal was a bit more difficult than I hoped.

The plastic casing above it didn't quite leave enough room to pull the terminal upwards without it snagging it (by a mm or 2).
In the end I approached it from the front of the car and pushed the plastic casing inwards with my thumb, whilst easing the connection off with my other hand.

Do you have a picture of the negative terminal?

I had removed the plastic cover under the bonnet.

What I could locate/ see is the brown cable terminal (i.e. the positive terminal).
Do you have a picture of the negative (Black) terminal?
Thanks...

(The pictures above are most likely from a US LHD car...)

 

[Porsche-Guru]

Had to do this today as second remote option didn’t work for me and our other Taycan had LTE. I’ll be honest I wasn’t looking forward to doing this as I’m not very good with this kind of thing especially on an electric car.

I decided I would do it and followed the instructions (which are superb!) and voila LTE is back. Thank you to @caslca for the in depth step by step instructions

Do you have a picture of the negative terminal?

I had removed the plastic cover under the bonnet.

What I could locate/ see is the brown cable terminal (i.e. the positive terminal).
Do you have a picture of the negative (Black) terminal?
Thanks...

(The pictures above are most likely from a US LHD car...)

 

[CaliPorsche]

Had to do this today as second remote option didn’t work for me and our other Taycan had LTE. I’ll be honest I wasn’t looking forward to doing this as I’m not very good with this kind of thing especially on an electric car.

I decided I would do it and followed the instructions (which are superb!) and voila LTE is back. Thank you to @caslca for the in depth step by step instructions

The picture in the start of this thread - with a red circle and an arrow pointing to it shows the negative terminal. At first glance it does not look like a normal ICE lead acid negative terminal, but once I looked closely the picture does a great job of identifying it … no5 sure if a car in blighty might have different set up tho with RHD.

 

[user959595]

Hi casica,
many thanks for the detailed in depth instructions!! So far, the LTE was not coming back. Therefore 2 questions where you probably already know the answer:
- you are stating that according to your manual the backup battery of the ConBox High will last for around 1 hour. Just for curiosity: in which manual is that stated?
- it is always said here around that the backup battery of the ConBox is charged only when ignition is on. Can you see in your manual maybe which fuse(s) are used for the ConBox and/or the battery and what other things are on it,e.g. if they are fundamentally needed for a while?
background: the Porsche dealer wants to have the car for every ConBox reset for 2 days and has to do a huge disassembly of the car due to the location of the box (justified with that a thief should not be quickly and easily able to just throw it out of the window). We would like to avoid this, but according to Porsche we have to wait with the 12V reconnection until the backup battery is empty.
If we can just kill the charging that would be the easiest way maybe...
MANY THANKS!!

 

[BigBob]

Do you have a picture of the negative terminal?

I had removed the plastic cover under the bonnet.

What I could locate/ see is the brown cable terminal (i.e. the positive terminal).
Do you have a picture of the negative (Black) terminal?
Thanks...

(The pictures above are most likely from a US LHD car...)

I found it impossible to disconnect terminal on mine (UK car). Trapped under some plastic lip. The only way i could see to do it was going to break something.

 

[Tooney]

Hi casica,
many thanks for the detailed in depth instructions!! So far, the LTE was not coming back. Therefore 2 questions where you probably already know the answer:
- you are stating that according to your manual the backup battery of the ConBox High will last for around 1 hour. Just for curiosity: in which manual is that stated?
- it is always said here around that the backup battery of the ConBox is charged only when ignition is on. Can you see in your manual maybe which fuse(s) are used for the ConBox and/or the battery and what other things are on it,e.g. if they are fundamentally needed for a while?
background: the Porsche dealer wants to have the car for every ConBox reset for 2 days and has to do a huge disassembly of the car due to the location of the box (justified with that a thief should not be quickly and easily able to just throw it out of the window). We would like to avoid this, but according to Porsche we have to wait with the 12V reconnection until the backup battery is empty.
If we can just kill the charging that would be the easiest way maybe...
MANY THANKS!!

I can't answer your questions about ConBox High battery. But if the problem you have is no LTE/datacomm in your Taycan, here is a link to a post with links to information and options for restoring LTE service:
https://www.taycanforum.com/forum/t...ssues-using-my-porsche-app.17709/#post-272507
The options have links to forum posts with details. Dealer resetting ConBox High is only one of the options available for restoring LTE.

 

[ionutz6]

I also got this LTE not available issue and planned a service visit, but meanwhile I found this forum and decided to try it on my own.
As i have followed the OP post (thanks for the great details!), I have left the negative terminal disconnected for 10 min, but nothing happened. No reset was performed, I reckon, as starting the car was identical to what was happening before this - user account there, time synced, no alarma etc.
I'm trying it again now with 30-min removel period. Is there an exact time interval where the reset is being performed? Is there also a limit for the disconnection (when is too long)?

 

[caslca]

I also got this LTE not available issue and planned a service visit, but meanwhile I found this forum and decided to try it on my own.
As i have followed the OP post (thanks for the great details!), I have left the negative terminal disconnected for 10 min, but nothing happened. No reset was performed, I reckon, as starting the car was identical to what was happening before this - user account there, time synced, no alarma etc.
I'm trying it again now with 30-min removel period. Is there an exact time interval where the reset is being performed? Is there also a limit for the disconnection (when is too long)?

That is strange. I've done this twice and both times a reset was pretty obvious, with various parts of the car recalibrating and the PCM also requesting calibration of the brakes.

Maybe a recentish upgrade made it so that more state is saved and doesn't reset on 12v power cycle the same way it used to a couple of years ago...

 

[ionutz6]

That is strange. I've done this twice and both times a reset was pretty obvious, with various parts of the car recalibrating and the PCM also requesting calibration of the brakes.

Maybe a recentish upgrade made it so that more state is saved and doesn't reset on 12v power cycle the same way it used to a couple of years ago...

In fact after waiting for around 30 min with the negative terminal disconnected, the reset was performed and even the LTE symbol appeared, so case solved!
The symptoms I have experienced after the reset:

- electric brake error - same as you mentioned
- electric window recalibration needed - same as you mentioned
- right chargin port error - I went and manually swiped the hand on the plastic wing and it worked fine

So all in all very happy with the result and with the fact that I had the guts to do it instead of waiting for local Porsche dealer to charge me hundreds of EUR for this.
And, of course, thanks a bunch for your clear and extremely helpful explanation!

Note: I suspect that the disconnect time was to be cumulated, so after waiting first time for 10 min, even a 15 min would have been enough the second time. In fact, after 15 min (on the second round), the car did not unlock by pressing the key, so probably the reset was already completed. Unless Conbox reset would require deep condensator drainige, as mentioned in some other thread. Just wanted to mention this for whomever might need it in the future..

 

[W1NGE]

I also got this LTE not available issue and planned a service visit, but meanwhile I found this forum and decided to try it on my own.
As i have followed the OP post (thanks for the great details!), I have left the negative terminal disconnected for 10 min, but nothing happened. No reset was performed, I reckon, as starting the car was identical to what was happening before this - user account there, time synced, no alarma etc.
I'm trying it again now with 30-min removel period. Is there an exact time interval where the reset is being performed? Is there also a limit for the disconnection (when is too long)?

5 mins is the recommended duration but check the Owner's manual.

It must reset given you've disconnected the power. All 12v systems will cold start.

Not a guaranteed fix but always worth a shot.

Disconnect for extended periods is not advised and could lead to other issues.

 

[W1NGE]

In fact after waiting for around 30 min with the negative terminal disconnected, the reset was performed and even the LTE symbol appeared, so case solved!
The symptoms I have experienced after the reset:

- electric brake error - same as you mentioned
- electric window recalibration needed - same as you mentioned
- right chargin port error - I went and manually swiped the hand on the plastic wing and it worked fine

So all in all very happy with the result and with the fact that I had the guts to do it instead of waiting for local Porsche dealer to charge me hundreds of EUR for this.
And, of course, thanks a bunch for your clear and extremely helpful explanation!

Note: I suspect that the disconnect time was to be cumulated, so after waiting first time for 10 min, even a 15 min would have been enough the second time. In fact, after 15 min (on the second round), the car did not unlock by pressing the key, so probably the reset was already completed. Unless Conbox reset would require deep condensator drainige, as mentioned in some other thread. Just wanted to mention this for whomever might need it in the future..

Good that it worked but the issues you got were due to prolonged disconnect period.

 

[ionutz6]

Good that it worked but the issues you got were due to prolonged disconnect period.

Well, tbh, since 10 min was too short for the reset, I couldn't have guessed the EXACT time that would reset the comm module, but NOT cause the other issues. And yet, those were not actual issues, they were fixed in less than a minute, so no problem.

Once again thanks to all for your comments that helped solve my LTE issue!

 

[nicks123]

I found it impossible to disconnect terminal on mine (UK car). Trapped under some plastic lip. The only way i could see to do it was going to break something.

Lost my connection to the Porsche servers last week driving back from Italy. A PCM reset didn't help and as it hadn't reconnected after leaving it for several days, decided to try disconnecting the 12V battery.

I had the same problem with disconnecting the terminal. But loosened the nut as much as possible anyway so it wasn't making a good connection, and left it for about 10 minutes before retightening. After various warning messages about electric brake not working, there was still no LTE symbol on the PCM. So I assumed it hadn't worked and locked the car. Came back to it 30 minutes or so later and magically LTE symbol was there - hurrah, normal services resumed!

 

[whitex]

I've always wondered why today's cars don't come with a master disconnect switch under the hood, one which would allow simple power cycle of all onboard electronics. "Turn it off and back on again" has been the oldest trick in the IT book for decades now.

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