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
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It's pretty much guaranteed your remote issue is unrelated to the limp-home issue.
It's also going to be impossible to determine the nature of the problem causing activation of limp-home without a trouble code. Considering the problem has only happened twice in ten months now, the chances of finding it without retrieving a code (and taking a guess based off that code) are near zero.
When you use the term "limp-home," do you mean that the transmission shifts to and stays in third gear, or that engine power is reduced to near zero.
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Thanks for responding hyundaitech, I don't know what gear it drops to, but last week it cut out as the service light came on just as I was ascending a mid grade hill. I had maybe 500' to go to get past the guard rail & onto a wider shoulder. The engine was running very rough & it was a chore to make it at about 5 to 10 mph. When I put it neutral , I thought it would stall & trying to rev it didn't really make much of a change -speeded up a bit but just as rough. As I said a quick battery disconnect for 30 seconds & then it fired right up & has run perfectly again for a good 800 km. of mostly mountain driving. I guess I'm just going to have to be sure to carry my code reader. The other odd thing is that the door locks are now working correctly -every time I lock the lights flash twice. For the previous month frequently the doors would lock from the remote but no flash & sometimes I'd hear a click but they didn't lock. Weird, I realize & yes most likely a red herring but then again the whole event is bizarre. BCinBC

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Since the engine performance is limited, it's definitely and engine control related issue. Typically, it's either with the accelerator position sensor, or some issue with the throttle body or one of its components.
Next time, try turning the car off and restarting. It may not be necessary to disconnect the battery, but rather just start a new key cycle.
-- Message posted using http://www.talkaboutautos.com/group/alt.autos.hyundai / More information at http://www.talkaboutautos.com/faq.html
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Thanks again Hyundaitech,

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I had a similar problem a few years ago with an XG300. They replaced the throttle body and it worked for a while, but went out again and the problem turned out to be a wiring issue and not the throttle body. Hyundai reimbursed me for the throttle body cost and once the frayed wires were repaired it ran ok.
Might want to check the wiring before major repairs.

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Thanks Dwight, The wiring on these cars is extremely involved. Do you have any idea as to where the wiring problem was located? Thanks, BCinBC

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don't recall, sorry

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