Recurring downstream O2 sensor issues

I have an '08 Tahoe w/ ~180k Miles. I've been having recurring issues with my Oxygen sensors on both sides, downstream (after the Cat). More often with the passenger side (Banks 2 sensor 2), which I have replaced, and I have taken it out a few times since and cleaned it with carb cleaner when my check engine light comes on (P2272 - O2 Sensor Signal Biased/Stuck Lean). The same code eventually comes back at some point. Last time I cleaned it was probably a month or two ago.

Now the driver side is throwing the same type of code (P2270). Same position, sensor 2 (after the Cat). So both sides are currently throwing a code. Are the sensors going bad, or is it an indication there's a bigger problem with the exhaust system? When I take the sensor out, it's pretty sooty, and if I stick my finger in the hole there seems to be some residue build-up on the inside...seems dirty and kinda moist, but it's an exhaust system and maybe that's normal for its age?

I notice I do have to top-off my oil once inbetween oil changes. Since I'm not leaking oil on my driveway does that mean I'm burining oil and that's why the sensors are getting fouled? Maybe my Cat is causing the problem? Motor sounds great, and no other issues.

Would you just deal with it and keep cleaning the sensors and then replacing them when they start throwing codes more often? Anyone else have this issue? Thanks guys!

For oil consumption
TSB 10-06-01-008M link:
https://f01.justanswer.com/ebrock63...il+Consumption,+MIL+ON,+Engine+Runs+Rough.pdf

and here a thread
https://www.tahoeyukonforum.com/thr...tor-oil-consumption-tsb-10-60-10-008m.108493/

jlatenight said:

I have an '08 Tahoe w/ ~180k Miles. I've been having recurring issues with my Oxygen sensors on both sides, downstream (after the Cat). More often with the passenger side (Banks 2 sensor 2), which I have replaced, and I have taken it out a few times since and cleaned it with carb cleaner when my check engine light comes on (P2272 - O2 Sensor Signal Biased/Stuck Lean). The same code eventually comes back at some point. Last time I cleaned it was probably a month or two ago.

Now the driver side is throwing the same type of code (P2270). Same position, sensor 2 (after the Cat). So both sides are currently throwing a code. Are the sensors going bad, or is it an indication there's a bigger problem with the exhaust system? When I take the sensor out, it's pretty sooty, and if I stick my finger in the hole there seems to be some residue build-up on the inside...seems dirty and kinda moist, but it's an exhaust system and maybe that's normal for its age?

I notice I do have to top-off my oil once inbetween oil changes. Since I'm not leaking oil on my driveway does that mean I'm burining oil and that's why the sensors are getting fouled? Maybe my Cat is causing the problem? Motor sounds great, and no other issues.

Would you just deal with it and keep cleaning the sensors and then replacing them when they start throwing codes more often? Anyone else have this issue? Thanks guys!

Click to expand...

Any exhaust leaks? If not, I'd start with replacing the sensors. That way, at least you "know" you're getting reliable readings. Still have codes coming up after that? It could be a few things, but I'd be pointing at the cats.

Thanks Hoe (heh)...no exhaust leaks that I know of. No indications. I took them both out tonight and cleaned 'em again. They were both pretty sooty, like a decent amount of black on a rag. I take back the moist part, seems dry inside. If the codes come back, I'll buy a pair and throw 'em in. You're right, maybe they're both just failing. Thank you!

These codes are usually due to a contaminated sensor. Did you clean or oil an air filter recently? Maybe use a gasket sealer around the intake, throttle body, air cleaner? Poor quality fuel could also cause this as could engine oil and coolant.

CIRCUIT/SYSTEM VERIFICATION

1. If any HO2S heater DTCs are set, perform those diagnostics first.
2. Allow the engine to reach operating temperature.
3. Engine running, observe the affected HO2S parameter with a scan tool.
 The pre-catalyst oxygen sensors value should vary from below 200 mV to above 800 mV and
respond to fueling changes.
 The post-catalyst oxygen sensors value should change more than 200 mV when the throttle is
quickly cycled 3 times from closed to wide open and back to closed after running the engine at
1,500 RPM for 30 seconds.
4. The affected HO2S may be damaged due to contamination. Prior to replacing the affected HO2S, inspect
for the following sources of contamination:


CIRCUIT/SYSTEM TESTING

IMPORTANT: All modules must be powered down or misdiagnosis may result.

1. Ignition OFF, disconnect the scan tool and wait 60 seconds to ensure all modules are powered down.
2. Ignition OFF, disconnect the harness connector at the appropriate HO2S.
3. Ignition OFF, measure for less than 5 ohms between the appropriate HO2S low signal circuit terminal A
and ground.
 If more than the specified range, test the appropriate HO2S low signal circuit for an open/high
resistance. If the circuit tests normal, replace the ECM.
4. Ignition ON, verify the appropriate scan tool HO2S parameter is approximately 450 mV.
 If more than the specified value, test the appropriate HO2S high signal circuit for a short to voltage.
If the circuit tests normal, replace the ECM.
 If less than the specified value, test the appropriate HO2S high signal circuit for a short to ground.
If the circuit tests normal, replace the ECM.
5. Ignition ON, install a 3A fused jumper wire at the HO2S high signal circuit terminal B. Toggle the
jumper wire between the HO2S low signal circuit terminal A and battery voltage. Verify the appropriate
scan tool HO2S parameter toggles between 0 mV and approximately 1,000 mV.
 If the appropriate scan tool HO2S parameter does not toggle correctly, test the HO2S high signal
circuit for an open/high resistance. If the circuits test normal, replace the ECM.
6. If all circuits test normal, replace the appropriate HO2S.

I have 210K on my 2008, no codes yet but if I wanted to replace O2 sensors pre-emptively, do I replace just the upstream ones or the downstream as well?

pacem said:

I have 210K on my 2008, no codes yet but if I wanted to replace O2 sensors pre-emptively, do I replace just the upstream ones or the downstream as well?

Click to expand...

This question asked and answered in the other thread of yours. No problem posting here though. When you do that sometimes, I found this out for myself, members here will see the old thread OP date and pass on by.