Hello,

I am confused. Do you know how many sensors do I need to buy and what kind?

Upstream, downstream, bank 1, bank2???

Best,
Michael

just replace the primary upstream wideband lambda on both head banks... two pieces in total.

Leave the others sensors alone unless faulty.

Thank you so much!! Is it hard to replace them? I hear I need to buy a special bold adapter. Would that help?

yes, you do need the $10 specialty socket. Replacing these sensors is well worth all the efforts.

The engine only runs as well as these sensors say it does. It's important to replace in pairs to keep engine banks balanced.

Enjoy the results as the ECU refreshes its fuel map. You'll get improved throttle response like new again.
✌️

There are wires coming out of the oxygen sensor so you need a special socket that had a slice in the side so the wires aren't cut. Otherwise there's nowhere for the wires to go when you put a regular socket on top of the oxygen sensor. Because it's an exhaust part, sometimes it can be hard to access and sometimes it's hard to loosen them because the heat has baked them on. But the new ones should already have some kind of grease on the threads so they can be changed out at a future date. As mentioned you only need to do the two upstream sensors. They're basically getting the raw exhaust before the converter so they do the most switching and wear out over time. The downstream ones don't really do much, they just monitor the results of the catalytic converter and the exhaust is cleaned up by the converter so they don't do as much work and don't normally wear out. When the upstream and the downstream have the same results, the computer knows that the converters are shot because they're not doing anything. You can sometimes rent the socket for free from various auto parts store like Autozone or O'Reilly Auto parts. You only change them out in the 100k range although the maker of the sensors say about 60-90k.

Thank you so much for the details. Mine is 4Matic (W212/E300/M276/2014). Do I need to need to remove the catalytic converter to gain access to the oxygen sensors? Thank you!

No, that would be a real nightmare. Usually the exhaust bolts are rusted on and if you had to remove them, you'd have to get new bolts. They're just in an awkward space because the upstream are just before the catalytic converters and the downstream are the ones after the converter. Haven't done them on your particular car so don't know how hard it is to reach them. Sometimes depending on the space you can get at them from the top of the car, sometimes you have to get at them from the bottom of the car.

I see. Thank you so much!

Hello, what led you to determine that you need new oxygen sensors? Are you getting a P0420? If so, let me know if that solves your problem.

You're talking about a crowsfoot socket, right?

The P0420 usually means your cats are toast. But there's other possibilities like a leaking exhaust or holes or bad oxygen sensors or just an occasional bad reading. Usually what that means is that the sensor readings upstream and downstream are the same which means the cats aren't doing anything. If one of the sensors were bad, that could be why the readings are the same but probably due to a fried converter which could be caused by exhaust leaks or misfires. This is why it's important to fix any problems before they get worse. Catalytic converters are expensive. Oxygen sensors are maintenance items, I'd replace the upstream ones once you're in the 100k+ range, you'd get better gas mileage anyway as they tend to get sluggish as they get older so the slightly better gas mileage would pay for themselves anyway if you keep the car long enough.

As for the socket, a crowfoot wrench would also work. Normally it's just a socket with the slice in the side so the wires can stick out. Autozone has a free loaner program so you don't even need to buy the socket/wrench just calls for a 30 deposit and you get it back when you return it.

https://www.autozone.com/test-scan-a...et/1103591_0_0

https://www.autozone.com/test-scan-a...ner/948079_0_0