04 Silverado, troubles with misfire and O2 sensor

[Carter Kelbert]

Truck is a 2004 Chevrolet Silverado 2500HD with the 6.0L V8 gas.

I am a little stumped with this one. I am getting P0156 (O2 sensor code), P0157 (O2 sensor low voltage Bank 2 Sensor 2), P0300 (random misfire)

I have been trying to fix the misfire thinking it was bad manifolds. Replaced the gaskets and the manifolds with headers, yet the codes all stayed. Then I replaced the O2 sensor Bank 2 Sensor 2. Even though I replaced the O2 sensor, I am still getting the same old codes... That means that it was not the O2 sensor itself and that there is another underlying connection, correct? I have a slight exhaust leak before the O2 sensor but it has a sleeve and clamp over it (still leaks a little but not much). Could this cause all 3 codes? 

Trying to get the old girl running right as I tow quite a bit with it and I feel like this is causing a lack of a lot of power. 

[CamGTP]

Both are circuit codes, the 156/157. For the hell of it check your o2 sensor fuses, make sure none are blown.

 

Also, rear o2 sensor codes on a truck like that won't effect performance as there are only there to monitor the cat. The truck will enable a cat test every now and then but again that won't change how it runs.

 

Upstream o2 sensor problems will make it not run good though.

 

The P0300 code means 1 or more cylinders are misfiring. You'd need a live data scan tool that will show what cylinders are misfiring. If you've never done spark plugs or wires, that may be a good place to start too.