I posted this earlier on a different forum, but they couldn't help me, so i'm copy pasting the text from that post over here:

My parents have a 2007 Volvo XC90 that a few weeks back got a problem with it suddenly loosing power. I had a test drive with it today and these are my experiences. The car starts out just fine, drives like a dream, no problems. But then out of nowhere, you will notice the car doesnt have nearly as much power as it should have. On lower rpm's its not that noticeable, but once you move up towards 2,5-3k rpm you really feel it. I tried flooring the gas, you could feel the downshift, rpm goes up as it should, but stops at 3k and doesnt pull any more than if it was running at 1,5k rpm. There are fault codes, but we don't currently have the opportunity to pull the codes ourselves, and getting it done at a workshop here in norway is crazy expensive, so i hoped someone here would have any ideas before we went there to check it out. If it is an easy fix we will do it ourselves of course.

Air filter is fine. My first thought was possibly a broken oxygen sensor? That the sensor does not give the correct readings and send it to the ecu, and the ecu then adjusts the air/fuel mixture to something completely off? I have never encountered such problems with a car before so i might be completely wrong here.

Also worth noting, i guess this has to be an electrical/sensor issue somewhere, as the car can drive with no problems for anything between 10 minutes to 10 hours, but can at any given time get this issue out of nowhere. Doesn't seem to have anything to do with driving style, uphill/downhill or anything else.

Thanks in advance!

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Edit: They did tell me however that the loss of power is caused by the car going into limp mode. Is this limp mode caused by any specific problems or could it be anything? Looks like i have to pull codes to get anywhere so i might buy an obd2 reader. Anyone has any experiences with bluetooth readers that you connect to your phone through an app, or should i get a whole unit with screen and everything?

 

While driving any distance over 60 minutes the car warning comes on saying sudden loss of brakes, stop safely. Airbag check light comes on. Within a few seconds all the electronics shuts down; all dash, stereo, lights, wipers, windows and lack of power to engine but car stays running. This was almost a deadly crash while driving in pouring rain and there were cars everywhere. No way to signal or flashers, I honestly thought me and my family were gonna get in an accident. I have read other stories online so my question is, What is the cause of this? How do I fix it before some gets hurt or even worse killed!I've contacted VOLVO and got no help. Been reading all sorts of things that"could" be causing this. I filed a complaint on the link below,there should be a recall on this. I own a 2004 xc90.



https://www-odi.nhtsa.dot.gov/VehicleComplaint/?