Reduced Engine performance

[sandphoenix]

Recently I got a 2004 Denali, it was cheap but didn’t run. The only real issue was a bad ground, but I redid the top end of the engine with new knock sensors, coils, plugs, wires, seals. I have a dealer level scanner and the only issue under the PCM is O2 heater performance. The air pump is bad and suspension control doesn't work (exhaust valve malfunction). When I engage cruise control the service suspension system message comes up followed by reduced engine performance; and the engine does into limp mode. No DTC follows. When I look through the major sensors they seem to be reading the correct data. I looked through these forms and couldn’t find my issue. Anyone have this issue or can point me to a tsb?

[Keitha5030]

Since it doesn't seem like any DTCs are being triggered or stored, It's difficult to say with certainty exactly what the cause is. But I've got basically the same truck (mine is a 2003 Yukon XL SLT) and i was experiencing and getting a lot of similar symptoms. Because i don't feel like writing a textbook this morning, I'll cut straight to the point, and if you have more specific questions just ask and I'll do my best to answer them. Are you by any chance having starting/charging system problems? On my truck i noticed that whenever there was rain or snow (water on the ground) and i was using my windshield wipers, if i didn't turn them off when i was parking for the night the next day whwn I'd start the truck, wipers would come on and i would have to pull the fuse to get them to turn off. I also started noticing that my "Air Bag" light was coming on  a lot randomly and intermittently. I was also having an issue with the battery that was in the truck, it would take and hold a charge, and crank it over without a problem, as long as there were no 10-15 minute periods of listening to the radio with doors closed and ignition off. Then my battery voltage would drop to 11.8-12.3 volts and the slow cranking would start. If the voltage dropped to a certain point, even when i managed to get it started WITHOUT a jump, the clock on the radio would reset to 12:00, the dual zone HVAC system would default back to 74 degrees etc. AND i would get the "REDUCED ENGINE POWER" message, truck wouldn't go faster than 15-20mph and all that good stuff. Every single time the system voltage dropped to a point, and that message came on, i would have to get my generic OBDII scanner out and clear the code(s) before it would run normal. And every single time it did that, it was always just 1 DTC that would be triggered and be stored P1517: (TACM) Throttle Actuator Control Module Performance. Im sure you know that these trucks have no cable from the gas pedal to the throttle, they are "drive by wire" there are a couple TSBs depending on the exact model, symptoms, DTCs etc but this should point you in the right direction TSB: 03-06-04-032 Here is a wiring diagram on the ETC (Electronic Throttle Control)