TTAC Commentator xyzzy writes:
One of the O2 sensors on my 1998 Lexus LS400 recently failed, throwing a P0161 OBDII code (at 175K miles). I’ve cleared the code and verified it comes back, so I don’t think it’s a transient failure. I haven’t yet replaced it, but I have noticed that my gas mileage, as reported on the trip computer, has improved significantly since the failure. Before it was 23-24 mpg, now I’m looking at 26. I know that one of the functions of the O2 sensor is to help regulate mixture, so I’m guessing the mixture is now leaner without one of the O2 sensors. I’ve noticed no discernable change in performance of the car. Assuming I can clear the error code before taking it in for OBDII emissions inspection, is there a downside to just leaving it and running aggressively lean (if that’s in fact what’s happening)?
If your O2 sensors have 175k on their tickers, you’re asking the wrong questions. But the answer to all questions is the same: replace the O2 sensors. That’s all four of them, partner.
Running old O2 sensors is like running an out of tune carburetor. Some manufacturers recommend changing them after 50k for peak efficiency, but I’d recommend every 100-150k for any application. (i.e. When your ride goes in the shop or you are motivated to spend some quality time underneath it.)
Even if the sensors are “good,” you can’t clear an OBD-II error code and pass an inspection: do so and the service tech gets a message saying the vehicle isn’t ready to test. So they’ll take your money for the privilege, then promptly fail your car…and ask you to come back after a week of driving. And, again, the code shall magically resurface.
Or conversely, it behooves you to do the right thing. Bite the bullet, and do a tune up (O2 sensors at the bare minimum) on this car.
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