My first generation Volvo XC90 3.2L gasoline engine gave an "Overvoltage Stop Safely" when I was driving up a mountain hill road, but first gave an "Anti-Skid Temporarily Off" message on the dashboard. There wasn't a place to stop right away as it was on a mountain hill, so a few other errors started showing up which I assume were a by-product of the Overvoltage error. These messages seemed to run the entire gamut of error messages for major system failures: Transmission Service Required, Anti-Skid Service Required, Engine System Service Required, Power System Service Required, and Overvoltage Stop Safely. The problem is that I was in a remote area with no cell phone service and had to get back home after canceling my plans. I did manage to drive the car back under a "Limp Home" mode, where many electronic things did not work. Such as the electronic windows, radio, transmission gear changing, dash display of what gear the car is in or even D for drive, and so on. And there also was a strong smell of what I guess was gasoline.
The voltage regulator was replaced with a new one, and that seemed to help the immediate error message on starting the car. The battery also was maintained by adding distilled water to at least the min mark. The "Service Required" messages are no longer there. I had wanted to put in a new after market Bosch alternator, but for budget reasons have temporarily only replaced the voltage regulator.
The problem: The "Anti-Skid Temporarily Off" message is still on. Did some electronic part get damaged? Or is there a simple reset? I do have an OBD 2 reader that I can use if that is helpful. With no English Haynes Repair manual for this Volvo XC90 SUV, I am asking the Forum for help. As the car is completely new to me. And budgets sort of mean that I need to try first to solve it and go to a Volvo mechanic second. Sorry about the blurry picture, as that was while trying also to drive up the mountain so it didn't autofocus.

 

Your first step would be a scan with a compatible scan tool that can talk to all of the control units in the car. Your OBD tool is probably limited to OBD (emission related only) codes stored in the engines and trans control units.

That complete scan will give you info as to what the control units think is wrong with the car. From that point depending on what codes are stored, you would develop a rational, reasonable diagnostic plan/procedure. Personally I would read, record if needed, and erase all codes first - then drive the car and see what codes come back.

 

Just had the same on my 2001 V70t5. Same messages with Battery, ABS,Brake, slippery condition lights on (see pics below). It would also drain the battery overnight. Put the voltmeter to charge point up front and it would show 16-17 Volts when engine was running at idle. Figured it might be the voltage regulator only that was bad since it was high voltage only. Tried to pull the codes and none was showing.
Went to a Pull-a-part place and found a 06 XC-90 with an alternator, pulled it off and replaced it with the alternator on my V70. 37$ and 10$ core return. Probably just needed the Regulator, but that would been more work and chance for something would go wrong.
Started right up and all messages and light are gone………time will tell if the battery reman charged in the morning.

 

Yes, the voltage regulator will keep the voltage generated from the alternator at the DC level for the battery. Since the alternator generates an AC voltage, the voltage regulator then converts it to a suitable DC level, typically about 14V or so. I also had to change the voltage regulator, and it was a bit of work to figure out how to do on the car since there is no repair manual in the aftermarket in English. Then a short while later, the "new" Bosch voltage regulator purchased from FCP Euro gave out. Then I bought a second "new" replacement Bosch voltage regulator again from FCP Euro. And I went and got a "remanufactured Bosch" alternator that looked to be a generic alternator from FCP Euro which had an unbranded voltage regulator on it and a tag that said something along the lines of "a bad battery can cause premature failure of the alternator". When I told FCP Euro, they refused to allow me to return the alternator even though it had not been installed in the car, and were completely unconcerned about it possibly being a fake Bosch alternator! I wanted to get a genuine Volvo alternator. Especially since to get the core charge back I think that I had to ship the core alternator at my expense back to FCP Euro and it didn't necessarily seem worth it to do so, considering that they may or may not approve the core sent in.

For this problem, a Volvo code reader isn't necessarily the first step. Especially if you don't have one. The first step is to measure the voltage with power off which is battery voltage, and measure the voltage with car running in park which is the alternator charging voltage. If it is well above 14V then change the voltage regulator. Or the entire alternator if you prefer. Also, it would be helpful for readers to give a suggested "Volvo code reader" if you suggest they use it as part of your solution.