So I bought a 2000 GMC Sierra 5.3l auto 4x4. 173k miles.
The first night I drove it home after buying it, the CEL came on after flooring the gas pedal. I check the codes and they are p0137 and p0157. "Low voltage" for "bank 1 sensor 2" and "bank 2 sensor 2" O2 sensors. So naturally the first thing I do is replace both downstream o2 sensors. No difference. CEL still lights up if you step into it a bit.
CEL will go away on its own after a period of time of normal driving, but will come right back if you give it 3/4 throttle or more a few times. Truck runs great as far as I can tell, doesn't seem to affect driveability. Not getting any other codes, just the p0137 and p0157.
Any ideas? The CEL is very annoying, and I want to get this problem fixed. Otherwise the truck is in great shape and I'm really happy with it.