I have a 3/4 ton 2003 Yukon XL with a 6.0L that I bought new. In Oct 2008 we started noticing the smell of antifreeze and eventually the truck went to reduced engine power and said to add coolant. I took the truck to the dealer that I bought it from and had it exclusively serviced at, and they concluded that I needed a new water pump and head gasket. $2500 later, I took it home and a few days later it went to reduced engine power again. I returned to the dealer who ran pressure tests on the radiator and they said it wasn't the problem. I asked them why it would keep going to reduced engine power and they said they didn't know and sent me home. I started going to reduced engine power on a daily basis, so I ended up getting a code reader. I recorded the codes and then erased them because my truck would only idle at reduced engine power- 5mph max. I went back to the dealer with the codes and they said there was nothing wrong...codes had to be present. Codes were P2135 and P1516. I researched these and after the dealer once again told them I wanted the throttle body assembly and wiring harness replaced and took along the detailed TSBs for them to follow. The service manager told me they couldn't do that because the truck was not currently producing the codes and that I would have the produce the truck with the codes present. I live 30 miles away from the dealership and have to use busy highways and interstates to get there, I could not safely idle at 5mph for 6 hours to get there. Lucky for that service manager, she went to lunch and I talked to a new service advisor. He told me he had seen lots of trucks with the same "reduced engine power" issue and replacing the throttle body and harness usually fixed it...so for $800 they replaced them.
Ok for a few months....then I start getting reduced engine power with the same codes again. I erase the codes and log them, hoping to find a pattern to present the dealer with so I can take it back in. I took it to a dealer closer to my home, mind you I had erased the codes, but had presented the service dept with them. This dealer was kind enough to give me a loaner and drove the truck themselves a few days hoping to go back to reduced engine power. After 3 days and no code, they sent me home with the truck. Next day it went to reduced engine power for me and I limped my way back. They said the wiring harness had not been spliced onto the throttle body correctly and I needed to replace that. Luckily I had only put 11,800 miles since the first one, so I did not have to pay for the part, only labor.
Went another couple months (mind you I don't drive the truck without the code reader now!), we were pulling out with the camper and DING DING DING Reduced Engine Power again. Noted the same P2135 code, erased it and drove home without issue. Every week or so I would get reduced engine power. I would erase and forget about it.
This past winter it started more frequently AND the truck would stall when it went to reduced engine power. I would lose all power steering and braking and almost got in a few accidents. Finally in February I took it in (with codes P2135 and P1516) and they said it was a ground. Replaced it for $150 and went home. Couple days later....Reduced engine power again....back to the dealer.....this time they said it had to be that wiring harness, so they replaced it again....$500...back home a day and now the reduced engine power again. This time it is additionaly throwing codes P0120 and P0220 in addition to the always present P1516 and P2135. Truck has been in the shop for almost 2 months now. They have inspected all the wires, checked voltages, replaced terminals and grounds, replaced module under the dash and it still goes to reduced engine power. I asked the service manager about the pedal position sensor and he said the codes they were getting weren't suggesting that.
The dealer said GM is not giving them any support, just telling them it has to be the throttle body and harness. The mechanic at this point has personally inspected every wire on this thing and I know he is just as frustrated as I am.
I can't drive this truck anymore as it stalls as soon as it goes to reduced engine power. I can't sell it knowing it is a huge safety hazard. Does anyone know what the cause of this could be?
Thanks for any new insights!!