Is it true

[gmaredd]

That when your service engine soon light is on that the truck goes into a so called limp mode or default mode? Will this cause the truck to feel terribly underpowered when under load.

[countryraised]

the engine light does not always mean it will go to limp home mode. but if it does go to limp mode you will have no power, it means "limp" home do not race do not tow, just get there.

[NCHornet]

Correct, only certain problems would cause limp code to be activated, and when it is, you will certainly know it!

[driximus]

my light is on now but its for the #3 glowPlug. I was feeling froggy mashed the go peddle, turbo lit, and tires spinned... wife went OMG! I said WHOOTS.

[BIGBILL105 45]

Originally Posted by countryraised

the engine light does not always mean it will go to limp home mode. but if it does go to limp mode you will have no power, it means "limp" home do not race do not tow, just get there.

When I wrecked, my limp mode came on and my truck didn't go over 20 mph.

[gmaredd]

Originally Posted by NCHornet

Correct, only certain problems would cause limp code to be activated, and when it is, you will certainly know it!

The truck seemed to run ok as I was pulling my snowmobile trailer until I came to any kind of hill, just didn't seem to have any power. Now, I also have my '97 that pulls very hard - but is far from stock(standard transmission also) and this is the first time I have pulled with the Excursion (auto trans). The reason for the question is that I have the ses light on with these two codes 1391 and 1393 and I didn't know if that would cause the lack of power. If this isn't affecting the power issue I am going to need some serious upgrades.

[NCHornet]

KC1 DTC P1391 AND P1395 RIGHT BANK, P1393 AND P1396 LEFT BANK AND P1994 CENTER MONITORING CIRCUIT. Both DTCs P1391 and P1393 together will set when the monitor indicates that all eight glow plugs are not being powered. An open in all glow plug circuits (shorted wire), the glow plug relay(faulty or inoperable), glow plugs(not working), Follow my write up on testing GP system to find out how many GP's are bad. There is a link to it in the Sticky "Winter Operation" at the top of this section.
GP's should not put the truck in limp mode, but we aren't even sure it is in limp mode. Do you have gauges? How much boost are you making? How heavy is the trailer and cargo? How steep is the hill? How fast were you going? etc.........