All O2 sensors go to 0 volts under acceleration P0420

[holeshotgmc]

The truck runs fine overall, I just bought it not long ago. It has 70k miles it's a 2014 4.3 auto 2WD so the LV3 and the 6L80 I believe are the correct numbers. I started getting random P0420 codes. It was every couple of engine cycles I was resetting it. Then for 3/4 tank of gas it didn't happen, today it came back. This time when it came back I pulled into a parking lot reset the light and opened up car scanner on my head unit and used my Bluetooth Amazon OBD reader to start seeing what the sensors were reading live... Keep in mind I literally just reset the light. I drove out of the parking lot I was in and got into the accelerator a little on the way out let's say 50 percent or so, heavy-ish acceleration, I saw all 4 O2 sensors drop to 0 volts and 0 short term trim and the code turned on almost immediately after that happened.

 

Any ideas?

 

When I don't mash the throttle the O2 numbers look normal front sensor fluctuates in the 0.1-0.9 range, back sensor reads around 0.8, mash the throttle they all seem to go to zero every time or every other time, let's say almost every time. The only code that has ever shown up is P0420.

Edited May 31, 2025 by holeshotgmc

[rlcole321]

Sounds like you might have a high pressure fuel issue.

GM 4.3L V6 EcoTec3 LV3 Engine Specs, Problems, Reliability, Oil

since it is direct injected, it has high pressure fuel pump (HPFP, driven off the cam) so if there is any fuel restrictions from the low side or high side, that might cause the symptoms you are seeing.