Voltage issue
 

I noticed my auto start/stop was not working. I did not spend time with this function during test driving the other day. I checked a few items, and a low battery or voltage could be the culprit.

My voltage readout with the engine running is steady at 12.7v, and when the engine is off it quickly goes to 12.3 and ticks down to 12.0...11.9, then I turned the key off.

Question: that engine on voltage seems a tad low. Should I be preparing to spend a couple days at the auto hobby shop? AllData says 14.9 hours for an alternator change on a 958 TT. That seems insane.

Or, would swapping the battery (intended to do anyway) potentially solve this issue? Gut tells me alternator, but praying for battery to be the fix.

Battery is shot

Exactly my thought too. Get yourself a quality AGM battery and a set of triple square bit socket attachments to get under the driver's seat where the battery lives. The auto start/stop feature will magically come back to life. And I'm willing to bet that after a couple of days of using it, you'll turn it off and never activate it again. I know where the car's starter is buried and with all that extra duty being placed on it to constantly start the car, it's certainly going to crap out sooner than later. Just my hunch. Besides, with all the electronics in the car, the battery drains down fairly quickly when the car turns off, so in my case the car restarts well before the traffic signal turns green most times. Especially since I'm in Southern California and the air conditioner is usually running in the background. The benefit of this feature doesn't feel like it's worth the risk in my case.

I 100% agree with start/stop. When they started becoming popular to save a gallon of gas a year, I told my wife we needed to buy stock in starter companies.

The seat heaters are also not working -- both flash the light once when I press them. I'm definitely thinking the two are related.

I made this a few years go with my 955. Is the process similar for the 958?

Checked Varta's website. This is the 958 battery: https://www.varta-automotive.com/en-...gm/605-901-095 It's nice to be 5 minutes from a Varta dealer. ;)

Most likely the battery. The voltage moves around a lot on these. You’ll notice it should jump up on braking and drops again on acceleration. Depending on the health of your battery that may behave a bit differently though.

You might try kicking it into sport and seeing what the voltage does. It appears sport turns off the economy strategy that varies voltage.

Either way I’d start with the battery.

Good news: New battery in place. Went with VARTA Silver Dynamic AGM 605901095. Voltage across a voltmeter was 12.85. Voltage displayed in Cayenne information panel when engine off is 12.8. Voltage while engine on fluctuates quite a bit, as mentioned above. Auto-start/stop works.

Bad news: All 4 seat heaters do not work. I found a thread on here about a temperature sensor. I will give that a shot.

Thanks.

Disregard that "supply voltage" -- Not sure what that is referring to but it certainly wasn't the battery.


I am not 100% sure, however, I think the interior cabin temperature sensor is at fault with my seat heater issue. Here is the readout from the "Actual values" interior cabin temp...

https://cimg7.ibsrv.net/gimg/rennlis...7ff96cf224.jpg

That's toasty!