Did this job yesterday. Had started it once before and then gave up because of trouble getting the CEM out. This thread was very helpful -- wish I could have seen the pictures but apparently my new account didn't have permission yesterday yet. Anyway a couple points for posterity (and compliments to mods here for not obsessively archiving threads!):

1) Getting the CEM back in was tricky. I ended up removing the ODB2 port which helped a bit. Part of the trouble may have been that the left side plastic "ear" of the CEM broke. The plastic on my CEM case was pretty brittle. With the outer lip of that ear crumbled away, it just kind of sits in the holder. So beware that you definitely want to read about the lever/tab/actuator on the left side that you need to push away toward the outside of the car when removing the CEM. If you just pull forward and down, as some guides suggest, you could easily damage the plastic junk.

2) Someone raised the point about the blob of "gunk" coating the chips. On close inspection, I concluded that the pooling of this gunk my 2 of my 4 chips, similar to the picture posted earlier in the thread in the bottom left corner of the main chip, was from excessive heat which damaged the coating. I made a small scratch in the coating planning to possibly remove it, and low and behold underneath appeared to be copper. So my idea - and I'd love to hear if it makes sense or not - is that Volvo for some reason attached a copper plate to the back of the chip as a kind of poor mans heat dissipation trick, and then coated with a polymer to mitigate EMF, and for good measure, added the metal cage. In the end, I didn't want to mess with the coating so I just attached my heat sinks to the back of the chips. If they get hot enough to melt that polymer, the coated surface will be hot enough to dissipate heat through the copper heat sink.

3) I did not use the same heat sink most people recommend here. I used a bunk of smaller ones and lined them up around the outer perimiter of the main chip, and there were enough to also cover both of the smaller chips. Here's where I got them if anyone is looking. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

4) Why didn't I put the heat sinks in the middle of the chips? Well, I don't really know. Call it intuition. I suspect that the issue is with very specific pins on the chip, maybe not having great connections. My gut tells me that's how applications like this end up with systematic failures - defects in chip manufacturing are pretty rare - defects in circuit board assembly as uber commonplace, and also that is where physical stress and heat cycling are likely to do the most damage. So I wanted to concentrate the heat dissipation around the pins.

5) Theories about what the "real" cause is: in my case, the first time this problem happened - "Left Rear Door Open" error, followed by loss of radio and total blanking of all instruments - we were driving through construction with lots of pot holes. I suspect the shock jarred something (e.g., a bonded connection), and that lead to a fault somewhere in the system. The number of "Alarm System Attention Required" and "Bulb Position Failure" alerts in these cars is ubiquitous. They all have them, and some when still very new. Electrical bonding and shorts appear to be - after "lifetime transmission fluid" - part of Volvo's planned obsolescence of these vehicles which are otherwise tanks.

6) Seat heater factor: Sometime shortly before or after the incident in #5, I noticed some discoloration of the leather in the passenger seat, and then also what appeared to be the kind of circular melt you would expect from a cigarette burn. Nobody smokes in the car, and usually the passenger seat is empty. After watching some videos about the in-seat heater filament repairs, I suspect in my case that may be contributing to "safe mode" fails as well. I suspect the fault in the seat wiring may be causing an over-current (not enough to blow the fuse, but just enough to make the chip directing that circuit to heat up). I reach this suspicion after having the "safe mode" problem trip while driving on the highway on a very cold day. Prior to that, I had only experienced it on hot summer days. As a result I decided to just pull the fuses from the L and R seat heaters. If your issue seems to correlate with something like seats/radio/alarm... then consider disabling those current draws by pulling the fuses.

7) Final thoughts on vehicle longevity: the fail safe problem doesn't seem to harm the car except for being a sore inconvenience in most cases. Originally I just carried pliers with me, and when it would happen on a summer day, I would pull off the road, disconnect the battery, and give it about 30 minutes and it cleared out. So basically a 30 minute coffee break. However, on the incident where I was driving on the highway in winter and had safe mode unexpectedly kick in, the thing that really bothered me (and why I resolved to fix it) was the transmission attempting to slam itself down to low gear while cruising at 65 MPH. Very bad. My car is still under 100K miles, and I've done a lot to make it last, including installing an in line transmission filter, running synthetic oil, and following a reduced oil change interval. So bottom line, if you have this issue appear in your car, be aware when cruising on the highway. Listen for warning signs and slow down BEFORE the safe mode nonsense kicks in.

I will try to follow up this post with the results after running the car this summer. If the home-brew heat sink solution doesn't work, I will do as others here and send of to those fellows in Canada. And on that note, I would add the following - the inability to economically fix this issue here in the US is inextricable linked to our IP laws and the snails pace at which they have not been updated. Anyone who is unhappy at the idea of "totaling out" their Volvo because a repair that should cost a couple hundred bucks will cost a couple thousand bucks because it can only be done by a dealership should most definitely consider throwing their political support behind the right to repair movement. Contract your US Senator / Representative. Tell them how you had to mail your car's ECU to Canada to get it repaired! This is a case where e-waste is an otherwise healthy car!