trouble with 8.1 ck engine light

[wwr]

i've got a 05 38j Itasca with the 8.1 runs good for 75 to 80 miles then ck eng light comes on engine is derated no power. codes are 131 and 141 lt and rt o2 senors low voltage i have changed fuel filter , both o2 sensors all plugs, wires, coils, exhaust dounts. still same issue it is normal on temp. i tried 60 miles everything good coming back three days later got twenty miles light came back on took scanner with me cked same codes,cleared got back home without codes again. cann't get into shop for a month or two do not know where to go from here HELP

[bigb]

Well it could be low voltage resulting from another sensor on the same harness shorted or otherwise bringing vref voltage down. You could try measuring vref on that harness and if it tests low then start unplugging other sensors to see if one of them is causing it. Assuming they only receive vref and are not heated? If heated they will need 12 volts and will be on a fused circuit but usually the code will be for a "heated 02 sensor" if that is the problem. They will still need vref though to communicate with the ECM.
There is more but I have to go pick up lunch, will be back

[bigb]

Back from Chik-Fil-A yum. Anyway I recommended the possibility of the short due to both sensors showing low, if just one shows low it is possibly an exhaust leak. Still possible there's a leak but less likely since both sides are reporting low voltage. Another reason is that exhaust leaks tend to close up as the engine warms up but you say the codes do not appear till fully warmed up and running awhile. An intake leak normally tricks the ECM into richening the mixture so I don't think that's the issue.
Not saying it's not an exhaust leak but I would look for a short first, in the wiring or in another sensor that shares the circuit. See attached video on locating shorted 02 sensor wires. Also Scanner Danner You Tubes are a great resource so check him out, I've learned a ton from him.

https://www.youtube.com/watch?v=U-M5CUcsc-E