Thread: 1999 Chevy Silverado 1500 O2 sensor problems

my friend has a 1999 Silverado with the 5.3 engine. he has been having issues with it lately. I scanned for codes, and there is a P0131, P0137, P0157, and a P0151, which are all related to front and back O2 sensors. there is also a P0300. my friend doesn't have money to pay a mechanic and so I'm trying to help him. I am not the best mechanic. I figured I would start on it tomorrow and check for any exhaust leaks. the manifolds are oem. I did notice on my scan that the LTFT is +25, and the O2B1 on the hp tuner chart is more wavy than my grand prix, like it isn't changing voltage very fast. I'll have to add all the other O2 sensors to read what they way.

I was wondering about that, I looked on the passenger side and didn't see anything, I'll check like you said.

I checked the o2 sensor fuses and they look good. I unplugged the mass air flow sensor and the fuel trims dropped to 0, and started to rise as long as there was no throttle applied. with a little throttle, whatever they were at before, they would come within +5 of 0.

I will take it for a spin around the block tomorrow and see how the truck does without the maf plugged in. I think if the maf reads wrong, then the o2 sensors are all going to be affected like they were.

I plugged the maf sensor back in and cleared the codes, and I couldn't get any codes to show up. the only problem I could see was that both banks of fuel trims were +25 most of the time. I took the truck back to the owner, and on the drive over, I went full throttle and the truck fell on its face. I let off and the truck continued driving like normal. this problem is definitely above my ability level to diagnose and repair.

Originally Posted by Fivefingerdeathpunch

Plugged cats or a bad MAF are likely causes.

wouldn't surprise me. I would rather let someone else diagnose it because I don't want to be responsible for wasted money.