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I just bought a 2003 GMC Sierra 1500 with 5.3L, auto, 4X4.

 

I was towing my trailer and it started acting like it had no power.

The 4X4 indicator button light was on 4 Low?

It took a long time to get to 55 MPH.

Drove that way for 30 or so miles.

Stopped and turned truck off.

When I restarted, it seemed to be OK.

The indicator light was back on 2 High.

 

Any clues?

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If it was acting like it had no power and said it was in 4low , the last thing i would have done especially while towing a trailer is take it to that speed.

 

Sounds to me like your 4x4 selector could be going out and switched it by itself..

 

I'd say if it happens again, pull over, restart it right away instead of risking damage driving that fast in 4lo

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I don't think it was actually in 4 Low.

The RPM was the same as when 2 High.

Plus the front wasn't working either.

 

 

I have had it show it was in Neutral once since then.

Still worked OK, though.

 

It never has shown any error message either.

 

:lol:

 

If it was acting like it had no power and said it was in 4low , the last thing i would have done especially while towing a trailer is take it to that speed.

 

Sounds to me like your 4x4 selector could be going out and switched it by itself..

 

I'd say if it happens again, pull over, restart it right away instead of risking damage driving that fast in 4lo

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limp home mode sounds like it was extremely underpowered and could not get up to speed very fast at all..

 

Did you hear your front tires binding or skipping at all while turning? Was the truck fighting you to turn?

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What is "limp home mode"? Never heard of that before.

 

 

Limp home mode usually happens when a major sensor malfunctions (MAF, coolant temp, electric throttle sensors, etc) or a very bad condition exists (overheating). The info center will display "Reduced Engine Power" and the truck will have very little power. It's basically a computer mode to protect the powertrain if bad things happen.

 

The truck most certainly wasn't in 4-low. You'd know it because the RPMs would be sky high and it would have tons of power from the low gearing. You'd also likely top out around 30-40 MPH. :lol:

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I believe the limp mode is something similar to what my boat engine has. It has a 302 cu in fuel injected Ford block engine. If the engine overheats or loses oil pressure, the computer will not allow the engine to operate above 1,000 RPM, which in a boat is very low speed (about 10 MPH). If the condition gets worse, the computer will retard ignition timing to the point where the engine will stall and cannot be restarted. I had this happen when my raw water pump impeller sheared and the engine started overheating. No damage to the engine occurred thanks to this system.

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Limp home mode is as was described.

The ECM falls back to a 'generic' setting to get it back home.

Not sure when they had this though.

My 2008 has it.

 

It definately didn't act like it was actually in 4 Low, no high rpm per mph.

No front end engaged.

Just seemed like the engine was being powered down.

No passing gear or kick down.

 

Today in fact I started out driving it and it showed it was in 'Neutral' on the 4X4 buttons.

It also had a slower power engagement.

Seemed sluggish until I got some speed up.

After a few miles it ran alright.

 

Thought there might have been some factory bulletins for this.

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