so i have a '03 h2 wirh reduce engine power. I've gotten my throttle body replace and the accelerstor sensor . A month ago two weeks ago "reduce engine power" happened again so i took it to the chevy dealer and thry said i needed a throttle body replace and o2 sensor. (2nd) throttle body totsl cost now $2300. Ok now reduce power again but i sware this onky hapoens when k hit a hard bump in the road but the truck isnt drive able after thst. No rpms and my engine sounds like a bad muffler can anyone please give me advice on whst could be wrong. Im getting it towed again today

 

I'd be pretty ticked with that dealer and would be demanding that they refund me for two throttle bodies it obviously did not need. An o2 sensor failing will not put it in reduced engine power mode and I'm not sure the throttle body can cause that either. I'f first suspect either the crank or camshaft position sensors. Maybe the throttle position sensor, fuel pressure maybe... I'd also check on the various GM truck forums. Those are far more common and use virtually the exact same engine and electrical systems and you will likely find a TON more people who have had the same issue with ideas.

 

Do you have the list of codes that appear when this happens, they can be a huge help.

There are a lot of things that can cause this, are the codes the same each time or are they random?

Neal

 

I worked on an 03 Denali that had random codes and would go into reduced engine power off and on. Turned out the front driver side wheel speed sensor had not been installed correctly and was grounding out on the wheel causing all the issues.

If the codes are specific to the throttle body and changing the throttle body didn't correct it I would look at the wire harness about 6" to 8" from the throttle body connector. Wiggle/pull on the wiring while the truck is running and see if you can make it go into reduced engine power or throw a code if so check the harness very close. If they are random its a bit harder to track down but you just have to stay at it.

Neal