O2 sensors are like spark plugs, they operate in a very harsh environment and they are recommended to be replaced at 100k miles, rarely are they.

If you choose to replace them, I would just replace the Pre-cat O2 sensors with Bosch direct fit units, usually Amazon or AutoZone/Advance online with coupons are a good price. If you can get them for under $45 each, this is a pretty good deal.

Now, the Pre-cat O2 sensors WILL not resolve the Lean codes, may even make them a bit worse. They may help with the SAP code(s), but the SAP system also has a few hoses that deteriorate and fail that will cause problems.

O2 sensors and the MAF are really the main controllers of the Air/Fuel mixture. The MAF is the single most sensitive and precise sensor on the vehicle, but ALL the fuel control is influenced by the Pre-cat O2 sensors. The measure or feed back what the fuel control system is doing so it can make corrections. So in the big scheme of things, healthy Pre-cat O2 sensors are important for a properly running engine.

If you wait to get OBDFusion and the interface, if the sensors are lazy, you will be able to see this and it may make you "feel" better when you replace them that they were lazy, but again, O2 sensors do not last forever and should be refreshed as recommended.

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2008 4.8i Black with Tabacco. Black Y-spoke wheels and shadowline trim.