Well maintained 2004 V70 with 130K miles. I drove the car last week from Nashville to Ft. Lauderdale (850 miles) with zero problems.

About 5-10 minutes into my drive to lunch yesterday, the car starts taking off really slow from red lights, like it's in 'limp mode.' I checked and the 'winter mode' button hadn't been pushed. I drive it extra easy, but it threw the 'transmission system service required' message. A few minutes later, it gives me a brake failure message, ABS and Brake light indicators turn on, and most of the gauges quit. Interestingly, the water temp, speedo, tach, and trip odometer stop working, while the gas gauge and the digital displays continue functioning normally.

I'll attach an image of what the dashboard looked like at the time. I'm traveling about 20-30mph when I took this picture.

At this point, I'm close to my destination so I park and eat. I figure the car can rest, and I can fuel for whatever I have in store for me. An hour and a half later, I start the car and see that the gauges are back, but it's now thrown an 'engine system service required' message. I'm a few blocks from Advanced Auto Parts, so I went over to get the battery checked and codes read. Battery and charging system are fine, and the OBD tool reported a PO600 (Serial Communication Link Malfunction), which is a general communication error, if I'm not mistaken. I reset the code and drove it 20 minutes home, and it appeared to drive normally.

I checked the ATF and it's fine. I drove it again early this morning, and even pushed it hard up to 50mph a few times and it runs and shifts just fine, with no messages and warning lights. I was going to take it up to Orlando tomorrow, but now I'm not sure that's a good idea. OTOH, I'm not sure why I shouldn't take it, since it's driving perfectly now.

It was too late in the day to take it to a shop/dealer, but I did call around to several volvo techs to try and make sense of it. Opinions ranged from battery/alternator, ABS module, faulty transmission, CEM, PNP switch, or something else entirely. I'm going to take it to someone get it checked out, but I was wondering if this kind of thing sounded familiar to anyone, or if anyone has ideas on how to start diagnosing the issue.

My main concern is whether this sounds like a transmission issue, or an electrical one. If it's the trans, then I don't want to drive it 3 hours and do further damage to it, plus the hassle of having a disabled car when I'm traveling. If it's a module going (like ABS), then I'm less worried about getting stranded, since it doesn't impact the drivability - just the stopability, ha ha.

Any insight is greatly appreciated.