Dreaded "Reduced Engine Power" issue

[tigers2007]

I have a 03 Silverado hd and mine says reduce engine power I replaced the whole throttle body and still goes in limp mode ?

Did you update the software? Either find someone with a Tech2 and laptop (or just an MDI and a laptop) or take it to the dealer.

[ifixedit]

The need to shut off your truck is an indicator of a situation that will only get worse.  In your case if you've never replaced the throttle body then it's probably due.  In the case of a new throttle body and it's still doing it could be several things, throttle body aside.  Key thing, don't start throwing parts at it and the codes you get may not necessarily point to the right thing!  Other areas of issue are the accelerator pedal assembly.  In my case I found that in 2003 Chevy must have made some mid year change on the gauge of wires leading from the pedal assembly through the firewall.  I determined that my original pedal assembly was junk and had a short in the plug at the pedal, wiggling it around with the truck running would produce the reduced power message, and even after replacing the switch in it 2x, still no luck.  I pulled a complete accelerator pedal assembly WITH the harness (important) out of a junk 2003 at the local wrecking yard, takes a whole 5 minutes to extract it.  Do not disconnect the harness, leave it intact if you can as this seems the more you disconnect and reconnect things it only disturb things further!  The plugs are very sensitive.  I found that the accelerator pedal assembly I pulled from the junkyard had a heavier gauge of wire than my original and looked to be a bit better made overall, so somewhere along the line GM figured something needed to be looked at.  I installed the pedal with harness that goes through the firewall and connects to the TAC (throttle actuator control) and this worked well until my cheap China made TB gave up the ghost again.  One of the codes you may get points to the TAC as being faulty.  This is the black box mounted on the firewall that the accelerator pedal harness plugs in to.  I will guarantee you if you get a code that the TAC is bad, it is not.  Don't waste your money buying a new one, it isn't the problem.  I found out the hard way on this one. 

 

So, other than what else I list below, the 2 main things to look at replacing is the TB itself, and possibly a good used accelerator pedal assembly with harness from the junkyard.

 

Other areas to look at:  The ground wires on the frame under the drivers side door, things here in MN cause it to get pretty crusty there.  The ground wire on the back of the drivers side cylinder head (royal pain in the rear to get at).  The plug that connects to the TB, make sure it is clean and dry and that none of the contacts in the plug have issues.  If it looks like the plug is questionable and some of the pins are not making good contact, they sell a pigtail harness at the auto parts stores.  As for the new TB, is it a good quality one?  I found  the made in China specials lasted anywhere from a max of 3 months to as little as 2 weeks.  They're all JUNK, don't buy a made in China TB.

 

Marc       

[pound41]

2003 Gmc 2500HD 8.1L Original owner. Only had the truck a few months. Cold morning started it drove to get coffee. Came out started and it went into REP.

Shook turn off the key turned it back on ran fine. Called the dealer he said not sure if it does it again bring it in. Was fine for years then that became the pattern. Only on the second start of the day.

Over the years it got to be more frequent. If I threw water on the throttle body connector it would start right up. TP 1 had the 5 volt reference but TP2 was 4.2 So we replaced the connector at the throttle body. After that it was fine for two weeks then it went into REP for the first in 16 years i while I was driving it. Grounds have been cleaned. Throttle body, pedal assembly, TAC and PCM replaced with new GM. Still did it.

Took it to the dealer they replaced some connector pins. Good for about 2 months the REP. I replaced the Plug at the TAC to see if that was it. Good for 2 weeks then REP mode. only thing left are the wires I guess