HELP!!!

[tomloans]

This one sounds like the ground behind the engine passenger side. it is likely broken. Tiny little wire bolted to the engine block. Ridiculous design. That little wire will cause all kinds of havoc if not grounded properly. Hard to reach the bolt but can be done with a little finagling. Also clean up the silver ground strap bolted to the drivers side firewall. Take it off and be sure to wire brush both sides of the wire and the bolt at the fire wall. You will see white dust coming off as you do.
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[michaelgoolsbyinf]

Long shot, but on my 03 Tahoe I was having same issue. I started it in my driveway one day and wiggled the throttle body Harness cables, then wiggled the connectors going to the TAC module. (On firewall drivers side) When I wiggled the 16 pin connector, it went into limp mode. I shut it off cleared code, started it and wiggled the connector again and it went into limp mode again. I found that 16 pin harness at lmctruck.com (I think) and soldiered that new harness in place. From that day on for about 2-3 yesar until I sold it, never had it go into limp mode again while driving. I did randomly get limp mode immediately after I started it, but shut it off, wait a few seconds and start it up and would be fine. Only happened maybe once or twice a month. Much bettter than unexpectedly going into limp mode while driving.

I wiggled every connection trying to get it to go limp mode, and can't. Every morning first start it goes immediately to limp mode. Reset, and good for a few hours, then once heat if day it's lime Every 10 minutes

 

[mwilson62000]

Sorry. Did you inspect the ground behind engine on passenger side Like @tomloans mentioned? It’s by the oil sender unit. Very hard to get to unless you pull the intake manifold. See pic. One on the left.

 

[mountie]

Sorry. Did you inspect the ground behind engine on passenger side Like @tomloans mentioned? It’s by the oil sender unit. Very hard to get to unless you pull the intake manifold. See pic. One on the left.View attachment 405953

Are those scary little ground straps the same on my 2005 Yukon 5.3 ??

 

[mwilson62000]

^^Yes.