XG300 goes into limp mode for no apparent reason

I have had my 2001 XG300 do this twice now some 10 months & 15,000 km apart. For no apparent reason the car will suddenly show a 'check engine' light & at the same time go into 'limp mode'. The car has only 115,000 Km (about 70,000 mi), has been serviced regularly & was/is running absolutely perfectly. On both occasions, I was driving highway speeds in a remote part of Wa state doing the speed limit & slightly accelerating. On the first event I was over an hour from anywhere with a code reader, so tried a momentary disconnect of the battery. The problem was immediately fixed. It ran perfectly for all these 10 months- I even carried my code reader with me for about 9 months in case it should happen again, but recently in getting the car ready for winter brought it in the house. So once again I had to disconnect the battery roadside (not fun at 6:300 AM on a cold desolate road). On both occasions there were no codes showing when I got home some 4 hours of driving later. Until last week, I dismissed the first as a fluke, but here it's happened again & I have no idea what to look for. By the way last spring I changed the plugs & checked virtually all electrical connectors that I could find under the hood. Everything looked good. The car starts quickly, runs smoothly, has all kinds of power & seems almost perfect. The almost is b/c at times the remote control for locking doesn't flash the lights even though it locks & once in a long while the alarm will sound even when opening a door locked & then unlocked with the remote. I mention this b/c when the car acted up last week, it also tripped the alarm after I had reset the computer, drove it for an hour,then stopped and opened the door -causing the alarm to sound. Any ideas folks?? Thanks, BCinBC