What did you do to your NBS GMT800 Tahoe/Yukon Today?

[Rocket Man]

Anyone have an idea?

I don’t know much about fuel trims but i would say something there isn’t right. STFT for B1S2 is over 99%?

 

[Fless]

@Tonyrodz

B1S2 (the downstream sensor on the driver's side) doesn't seem to be awake. Is that one new? If the voltage constantly sits around 450mV it's not waking up. Can you see if the truck is going into closed loop? Check the power to the O2 heater circuit.

EDIT: would love to see graphs of the upstream and downstream sensors when the truck is warmed up.

 

[MassHoe04]

Anyone have an idea?

Unplug the upstream O2 sensor and see if it runs better. If it does, the sensor is bad. Replace, if necessary.
If that has no effect, plug it back in and check the top side for possible vacuum/air leaks.

Also... With reading that high, there should be a CEL. What code(s) do you have?

 

[MassHoe04]

@Tonyrodz

B1S2 (the downstream sensor on the driver's side) doesn't seem to be awake. Is that one new? If the voltage constantly sits around 450mV it's not waking up. Can you see if the truck is going into closed loop? Check the power to the O2 heater circuit.

EDIT: would love to see graphs of the upstream and downstream sensors when the truck is warmed up.

That might be something to look at.
But the downstream O2 sensors don't do anything that really impacts the engine running good or not. Upstream sensors have the most significant role in the computer's control over fuel/air.
I would try briefly disconnecting the upstream sensor on that bank, just to see if that makes the engine run better or not. No cost to rule out a bad sensor.

 

[Tonyrodz]

Pretty sure I replaced the ps O2 sensor, which @Scottydoggs helped me to diagnose--actually he diagnosed. My down stream O2's are tuned out, so nothing to worry about there. The only code I have is a maf sensor, P 0103. I've swapped to a known good maf with no change. It's a "soft code". It doesn't light the cel, but it's always there when I scan for codes. Been there since I got it tuned--tuner was an ice hole lol.

 

[Tonyrodz]

@Tonyrodz

B1S2 (the downstream sensor on the driver's side) doesn't seem to be awake. Is that one new? If the voltage constantly sits around 450mV it's not waking up. Can you see if the truck is going into closed loop? Check the power to the O2 heater circuit.

EDIT: would love to see graphs of the upstream and downstream sensors when the truck is warmed up.

How could I tell if it goes into closed loop?

 

[Fless]

How could I tell if it goes into closed loop?

Your scanner should tell you in the menu that displays powertrain values. Your Tech 2 would show it.

Here are the O2 heater fuses to check if you are so inclined (O2A is for front; O2B for the downstream):

 

[Scottydoggs]

Anyone have an idea?

your tech 2 should be able to show you the same things i used to scan the o2's. your looking for the o2's in Mv. and the fuel trims of both banks to really tell.

if the other side went bad i sure hope the bung dont twist out again.

tech two should also be able to tell you when it switched from closed to open. normally thats when it comes up to operating temps, or on its way there.

 

[Tonyrodz]

your tech 2 should be able to show you the same things i used to scan the o2's. your looking for the o2's in Mv. and the fuel trims of both banks to really tell.

if the other side went bad i sure hope the bung dont twist out again.

tech two should also be able to tell you when it switched from closed to open. normally thats when it comes up to operating temps, or on its way there.

I was thinking the same thing. I'm tempted to just take it somewhere to swap out the O2. I don't really want to deal with that again.

 

[Walchit]

The flashing MIL was a random cylinder misfire code.

Been watching cam bearing videos, I guess my first step is buying a cherry picker.