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

 

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.

 

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

 

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.

 

Thanks again Hyundaitech,

 

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.

 

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

 

don't recall, sorry