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I sure like this idea and hope it catches on.

From caranddriver.com:
Hyundai, for instance, considered the absurdity of jump-starting an electric car or hybrid and connected its low-voltage systems to the large traction battery, allowing electrified Hyundais to jump-start themselves when you push the "12V Batt Reset" button on the dash. And while that button conjures an image of your standard AC Delco lead-acid, the low-voltage systems are actually run by a 14-volt lithium-ion battery that sits inside the high-voltage battery pack. You won't find that at the local auto-parts store.

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Is the reset a reset or a jump start?

I am betting it is a temporary disconnect and re connect something I have been wanting the P8s to have for months.

Or it could be a restart where it actually draws power from the big battery.

Nice find though and I would love to have both buttons.

The former reset would show there is and help with instability in the software /hardware.

The later would be acknowledgement that the car can get into a mode where it drains the 12volt. This has been reported in multi brands of evs.
 
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'21 XC40 Recharge P8 Sage Green
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I sure like this idea and hope it catches on.

From caranddriver.com:
Hyundai, for instance, considered the absurdity of jump-starting an electric car or hybrid and connected its low-voltage systems to the large traction battery, allowing electrified Hyundais to jump-start themselves when you push the "12V Batt Reset" button on the dash. And while that button conjures an image of your standard AC Delco lead-acid, the low-voltage systems are actually run by a 14-volt lithium-ion battery that sits inside the high-voltage battery pack. You won't find that at the local auto-parts store.

View attachment 3582
So if the 12V battery is dead - then what runs the relay that engages the high-voltage battery, when you push that button? Yet another low-voltage backup battery?
 

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I only get about 185 usable miles as compared to the 220 miles claimed by Volvo.
As they say "Your mileage may vary". Driving at what speed? In what temperature? Hills or flat terrain? 100% charge or 90%? Running the AC/heat pump?

I would say 185 miles is within normal range variation.
 
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Also max is the range from 100 to 0

Reality normal max is more like 90 to 15.

Is this 185 miles impacting your life Oscar?
 

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So if the 12V battery is dead - then what runs the relay that engages the high-voltage battery, when you push that button? Yet another low-voltage backup battery?
I believe this quote from the article is the clue " And while that button conjures an image of your standard AC Delco lead-acid, the low-voltage systems are actually run by a 14-volt lithium-ion battery that sits inside the high-voltage battery pack. "
 

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I don't even fully understand why there is a need for a 12v battery either. I get many of the legacy car systems are designed to run off 12v, but surely they could just use an inverter and step down part of the high voltage battery to 12v to run these systems. That would save having to carry around a heavy lead acid (or whatever) battery up the front and would prevent anybody from having a "flat 12v battery" every again.
Agree, they don’t even have to have an inverter since the Li + is DC current. A simple transformers will do it. The XC40 Recharge requires special towing when there is no power at all. We can’t select the “tow mode” when there is no power. I also agree with you that the -2 volt battery drives the older electronics in the system; inherited modules from years past. Thanks for sharing this info and hope my battery issue is resolved within a reasonable time.
One other issue is that EV technicians are few; not all dealerships are equipped to handle this technology. Here in the Miami area we have zero proficiency technicians. They rely on Volvo headquarters support via internet and phone. Totally unacceptable support.
 

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There is an assumption that all of the "power failures" are secondary to the 12v battery being depleted. This is not the case.

I had five complete power failures. On an attempted start, there was no power. It was still possible to access the IHU screen but tow mode would not engage and keys would not unlock the doors.

The car did show at least an 80% battery charge and the 12 volt battery had a full charge. Jump starting did not fix the issue as the battery was fully charged.

A trickle charger did not solve the problem.

These issues are more than just a bad 12v battery. It is a combination of software/hardware/firmware that is not stable in all cases.
 

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There is an assumption that all of the "power failures" are secondary to the 12v battery being depleted. This is not the case.

I had five complete power failures. On an attempted start, there was no power. It was still possible to access the IHU screen but tow mode would not engage and keys would not unlock the doors.

The car did show at least an 80% battery charge and the 12 volt battery had a full charge. Jump starting did not fix the issue as the battery was fully charged.

A trickle charger did not solve the problem.

These issues are more than just a bad 12v battery. It is a combination of software/hardware/firmware that is not stable in all cases.
Was your case ever resolved?
 

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Agree, they don’t even have to have an inverter since the Li + is DC current. A simple transformers will do it. The XC40 Recharge requires special towing when there is no power at all. We can’t select the “tow mode” when there is no power. I also agree with you that the -2 volt battery drives the older electronics in the system; inherited modules from years past. Thanks for sharing this info and hope my battery issue is resolved within a reasonable time.
One other issue is that EV technicians are few; not all dealerships are equipped to handle this technology. Here in the Miami area we have zero proficiency technicians. They rely on Volvo headquarters support via internet and phone. Totally unacceptable support.
You can jump start the 12v battery like any car. As Homer noted above sometimes there are additional issues but if it’s just a dead 12v you can jump it. There are dozens of videos on YouTube of owners of every type of ev having to jump their 12v after power failure.
 

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Was your case ever resolved?
The explanation given to me by the dealership, which was passed down from Volvo technical support, came after five days of diagnostic telemetry.

They claim there is a unknown or ill defined component which is being activated at some ill defined or unknown time interval. This causes
a system wide power drain and results in the power management software to shut down the entire power system.

What is bizarre is that this seems to happen about every six weeks.

An ill defined and future software upgrade may or may not resolve the issue.

Volvo has accepted the fact that the car is not fixable at present and has repurchased the car.

I continue to occasionally post as I did enjoy the car when it worked. I considered another XC40 or C40 but am not convinced these power issues and reliability problems have been
resolved.

I am considering options on a new XC40 in the future. However, I will wait until I have evidence of stable software and hardware.
 

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Just a thought, but the problem took place in January. Could it be that the traction battery was being conditioned due to cold temperatures? I believe the main AGM and TCAM Li batteries charge when the car is online, either from the car being in active state or when charging the traction battery. Yes, things need to improve but perhaps comparing a fossil car to an EV is part of the issue. We probably do need to make sure the car is in a high state of charge in winter and it’s scary when your car dies with no clue as to why, regardless of the juice that powers it.
 

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I am baffled. I get disconnecting the HV battery, but honestly have an isolated step-down to 12V tap that runs the car and shave another 50+ lbs off the weight of the car and these stupid issues.
 

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The 12 volt standard is there for accessories like windshield wipers, HVAC fans, door locks and window lifts etc common to all cars. Changing that is like turning a supertanker around. The electronics nominally run from 12 volts, but step down for microprocessors, LEDs and so on. Stepping down from 400 volts requires big transformers and efficiency loss from a battery they are milking every last watt of energy from, so they charge the AGM instead. Then there’s the fact that they use AGM batteries as they are less sensitive to low temperatures than lithium ion. It isn’t perfect but I think there’s method to their madness. Even Tesla uses 12 volt systems, and they’ve had 12+ years to figure it out.
 

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The explanation given to me by the dealership, which was passed down from Volvo technical support, came after five days of diagnostic telemetry.

They claim there is a unknown or ill defined component which is being activated at some ill defined or unknown time interval. This causes
a system wide power drain and results in the power management software to shut down the entire power system.

What is bizarre is that this seems to happen about every six weeks.

An ill defined and future software upgrade may or may not resolve the issue.

Volvo has accepted the fact that the car is not fixable at present and has repurchased the car.

I continue to occasionally post as I did enjoy the car when it worked. I considered another XC40 or C40 but am not convinced these power issues and reliability problems have been
resolved.

I am considering options on a new XC40 in the future. However, I will wait until I have evidence of stable software and hardware.
Excellent post. Thank you.
I am heading down a similar path. After 5 weeks my C40 had a complete power system shut down. Tomorrow will mark the completion of six days of diagnostics with Volvo technicians. The 12V battery was fine. Strangely, a 175amp fuse was blown. Their current thinking is to continue analysis to avoid my experiencing a recurrence. I'm not sure what to think currently.
 

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I am baffled. I get disconnecting the HV battery, but honestly have an isolated step-down to 12V tap that runs the car and shave another 50+ lbs off the weight of the car and these stupid issues.
All fine and dandy if you’re on a car platform designed purely for EVs (next generation Volvos maybe). But not on a shared ICE/EV architecture like current XC40/C40/Polestar2. One of many compromises.
 

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Excellent post. Thank you.
I am heading down a similar path. After 5 weeks my C40 had a complete power system shut down. Tomorrow will mark the completion of six days of diagnostics with Volvo technicians. The 12V battery was fine. Strangely, a 175amp fuse was blown. Their current thinking is to continue analysis to avoid my experiencing a recurrence. I'm not sure what to think currently.
Helluva lot of current for sure! ;)
 

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The same thing happened to my XC 40. I was away for 10 days and the car went into “sleep mode” as the Volvo “on call” person called it.
Oscar
I, too, was worried about the low voltage system (12v battery) when I was gone for a while. I was away for 10 weeks and had no problems when I returned. I followed the VC advice on LT storage (I.e., plugged in, charge set to 50%, and car locked). The car went into “sleep mode” but it was more like “comatose mode”. When I powered up the center display had a message about restarting from “battery saving mode” or something to that effect. I lost app connection after three days and it did not re-establish until I returned — BT connection.
 
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