According to my mother the radio has not been working correctly and kept disconnecting from her phone.

I noticed the next day the radio was flickering on/off, and then the brake failure warning appeared on the dash, but I could still drive it and they stopped appearing after a while.

The next day it gave the brake failure and anti-skid errors. When I tried driving it, a few times it would just cut out. After a few attempts of driving for a minute and it cutting out, it refused to start. After leaving it for 30m it started and drove it in a low gear around the block and back to the house.
I checked the battery and it was 12.6v. After starting the car, it would go up to nearly 15v, and then down to 14.82v.

Going off suggestions here, the CEM was removed and inspected. All seems good connectors wise and no corrosion, but two of the fuses: 45,57 had blown.
Tried changing these to see what would happen.

After reinstalling the CEM, it got worse. The car now gives an immobiliser "try start again" fault and won't let me start. Has it actually lost programming after being removed for 30m?? And the wipers won't turn off!

Not sure what to do now, any help is appreciated.

Update1: Reinstalled CEM again, after a few tries the immobiliser fault went away and the engine struggled to start. After that it doesn't do anything when you turn to the start position. It doesn't make the 'zap' noise like it used to either when you insert the key, though i'm not 100% if this just went away now or when the problems began.

 

Check your voltage again. If the car is making 15 volts while running, that's too much (and that can mess up a lot of things - though honestly it's not likely if it's a "clean" 15 volts, rather than a spiky, messy waveform coming out of the alternator).

 

Car won't start as noted in the post so I can't check again. When idling the voltage was 14.88-15.02v something between there.

 

But I assume the voltage on the battery (car not running) is still over 12 volts when you're trying to start it. 15 volts IS too high, but could also be because of an inaccurate voltmeter (wouldn't be the first time). If it really IS 15 volts, the headlights should be "unusually bright" though that can be subtle.

I think the key is in the blown fuses.

45 is a "power socket", which I suspect is your cigarette lighter plug, and most likely due to something that was plugged in (defective, or drawing too much current).

57 is to your brake light. If something is wrong in your brake light circuit, it's like your foot isn't on the brake pedal, so it won't spin over.

I'm thinking the problem is likely something wrong with the CEM, since things seemed to change when you R/R'd it. Any chance it may have gotten wet (not unusual)?

 

When engine is off it Is 12.X volts. I should add that the wipers are going off themselves too and it's a 2012. The CEM is like new, no corrosion or water marks, nada. Double checked the wires are secure but can't see if there's any damaged after the connectors.

No idea why the fuses went as 57 is also OBD, and the cheap one I had wouldn't connect. Now it does but it can't read it anyways, guessing needs a Volvo proprietary one.

I'll ask if the lighter wasnt working before it stopped starting or if that happened since it went kapoof.

I did get in it and it didn't give me an imobiliser fault but would splutter and not start. When I came back an hour later it went back to immobiliser fault and refused to try and start. Sometimes itlll show the trip mileage sometimes it won't.

Not sure what to do or who I can bring out, and if it's even worth it.

 

A generic OBD reader should work just fine (yes, it won't do the "proprietary Volvo stuff", but will read / delete codes, and check other parameters just fine).

The fact that's not working makes me suspect the CEM even more. I'm pretty (but not entirely) certain that the OBD is connected to / through the CEM.

Replacing a CEM does require the dealer reflashing the new (or used) replacement (double-check this, though I'm pretty sure).

There are also businesses out there who specialize in repairing things like this, and will avoid going through the Volvo stealership (though the fix might not be cheap).

 

So a little update.

I got one of the better diagnostic scanners and gave it ago. I had left the car for a while and this time it started just fine and after a minute the brake failure, anti-skit faults came back. Revs went to 0, limp mode, etc.
The scanner shows many loss of communication faults such as to the steering angle sensor, CEM, ABS, etc.
The scanner has the ability to scan the CEM and CEM-low. CEM-low shows something about the main battery relay, general electric fault. While the CEM won't let me scan. Is that a sign of anything perhaps? Red herring?

The voltage on the scanner (which must read from the computer) flickers through a range of values quickly but generally shows 13-16v. I would try the voltmeter again today (a few days later), but since fiddling around the battery has dropped to 10v and requires a jump start to get going. And I'm kinda done messing around with it.
Every time it's left for a while, it will let you start up and move off for a couple of meters or more and then remember the fault. Sometimes then it'll prevent you from starting or not.

At this point, not sure what to do. Not sure who I trust can fix it without being a money pit.
Advice as always appreciated

 

I'd throw a real voltmeter on the battery line. The flickering values you're getting from your scan tool doesn't sound quite right.