I've got a 2021 XC40 T5 AWD Momentum in the U.S.
I bought the vehicle used 2 months ago with 48,800 miles on it. The Start Stop function has worked only 1 day for me.
So far I have not done a lot of long distance driving so most trips are 10-20 miles or less. However I have put the Main battery on a charger twice and it apparently fully charged the battery both times. The dealer told me that the support battery is charged by the main battery and that they've checked both batteries and that they pass.
I've been struggling with the Volvo Dealer to figure out why Start Stop is not working. I get the excuse that there are many conditions that must be met for it to work so "obviously" one of the conditions is not being met. Well, the car was a Volvo Certified Used Car and the function only worked one day. Hard to believe that all the conditions haven't been met except for the 1 day that it worked. It's not winter (too cold), it's not summer (too hot), the main battery is fully charged. Not sure how to even check the support battery charge, but there are no codes being thrown, nor are there any error messages in Sensus.
Soooo, after continued badgering with the service department, they have finally escalated my case and contacted "Hotline" whatever that is. Still waiting for info from the dealer. They've had my car for 3 days. Very frustrated.
I've visited several XC40 forums, Reddit, and Facebook XC40 pages. This seems to be a recurring discussion on all these forums. I've read that software updates broke the stop/start function, I've read that software updates fixed the stop/start function. I've read that the support battery has to be at least 80% for start/stop to work. I've read that the support battery has to be at least 85% for it to work. I've read that having anything connected to USB, like my iPhone, can cause enough battery draw to prevent start stop from working... or having a dash cam connected. I've only had my iPhone connected and don't have a dash cam. And how could having just an iPhone connected via USB use a meaningful amount of battery power anyway?
So I wait and hope that Volvo figures out what is going on. I'm not optimistic.
