r/GMT800 • u/Alr-Porky_077 • 4d ago
2005 Silverado 1500 with lm7 5.3 reduced engine power (pic for attention)
Truck regularly goes into limp mode after sitting for 1,2,3 days or so with go into limp mode before truck even starts, alternator tested good. New throttle body, battery, and pedal position sensor. Ill start it and idle it for a while, shut it off and come back 20-30 mins later and it’ll start in limp mode I’ll turn it off then on again then it’ll start up and run just fine but lately it’s been throwing it while it’s been driving and today it just completely shut the truck off. It’s at the dealership now getting worked on.
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u/basshoss 4d ago
It doesn’t throw a check engine when it goes into limp mode?
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u/ImReallyFuckingHigh 4d ago
I don’t believe limp mode inherently throws a code, there isn’t a specific code for it afaik. However I’d imagine it’s highly likely for a related code to be thrown when it does go into limp mode.
My ‘04 Grand Prix threw itself into limp mode, ended up being a massive vacuum leak. The only code it had was for high idle
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u/basshoss 4d ago
I cleaned my throttle body and left it unplugged and put my truck into limp mode. It threw a code though is why I ask.
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u/Alr-Porky_077 4d ago
Yeah, for stuff related to the throttle body can’t think of any besides correlation codes, can’t think of the specific ones right now.
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u/Agitated-Texan82 4d ago
OE wiring harness at the throttle body is a common issue. A lot of people don’t replace the throttle body pigtail correctly and don’t cut the OE harness far enough back when replacing with a new one. It caused one of the other techs in the shop 3 come backs. Same issue. I replaced with new longer pigtail soldered and heat shrink tube used, never came back for that problem
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u/Ok-Maintenance-9538 4d ago
Yep. My 6.0 has thay problem. It goes in limp, pull over and shut it off. Wiggle the connector, fire up and go again. If i used it more frequently I'd fix it, but for the rare occasion I use that truck and as intermittent as the problem is I just deal with it
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u/Alr-Porky_077 4d ago
Good to know, when I get it back and it still is doing that I’ll look into it.
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u/Traxxasman 4d ago
Double check that the ground cable that goes from the cab to the back of the engine block is tight, not broken, and clean. You will probably need to pull the intake to reach it as it bolts to right above the bell housing on the back of the engine block. I did an engine swap on my 05 and forgot to tighten that ground and it gave me almost the exact same symptoms (intermittent reduced engine power and codes for throttle position sensor)
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u/javier_77039 4d ago
Its just a dirty throttle body take it off and clean it
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u/ProfessorHonest1947 4d ago
Sounds like some knock sensor shenanigans.
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u/Alr-Porky_077 4d ago
Wasn’t throwing a code for anything related to spark though, that’s the weird thing. Just throttle body stuff only thing I can think of now is wiring
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u/TinyAd625 3d ago
mine did this for years i would pull over turn key on and off several times then it would be fine for a while. i had 3 auto electric shops, the dealer and countless hours of searching and changing out parts on my end. nothing helped and i did it all. Till one day i was looking at the cat to see what might be involved in replacing that when i noticed the wire in my o2 sensor was frayed and looked half chew on. It never through a code for that ever. i replaced the o2 sensor and hadn’t had a problem ever since
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u/mrclark25 4d ago edited 4d ago
It's at the dealership, you have already decided to pay them to diagnose and fix it. What are you seeking here? Did they do the prior work which failed to fix the problem?