[obadran]

I have a general question on how O2 sensors work.

96 Yukon 110000 miles

Is it normal for both upstream sensors to output zero volts under a hard accelaration (ie. trying to merge into 70mph traffic)?

I'm having this problem with a lack of power and I noticed that when I "punch it", the engine hits somewhere between 3000 and 4000 rpms and then starts hesitating and VERY SLOWLY the rpms climb...also during this little test, I notice both upstream O2 sensors drop to zero volts and the computer goes into OPEN loop mode. If I do this test long enough, the SEL comes on with P0131 and P0151 codes (O2 sensor low volts sensor 1 banks 1&2).

Could this be faultly O2 sensors or could it be a fuel delivery issue that runs the engine so lean that the sensors are reading correctly?

I'm also starting to wonder if some of the sensors are starting to fail given they are all 110000 miles old.

Thanks,
Omar