Replacing Oxygen Sensor
 

My 2006 LR3 V8 SE with 86k miles got the check engineer light. Since it's just P0174 without P0171, I assume it's the oxygen sensor. Bank 2 Sensor 1, so it's the driver side front/upstream (please correct me if I'm wrong). Anyways, the new sensor arrived today but couldn't get the old sensor off. I can see the it from underneath the car and I think I can loosen it with a crescent wrench, but I could not disconnect the wiring. My fingertips barely reach the connector and my forearm gets stuck and could not reach in any further. Started getting dizzy after half hour of trying. Even if I could somehow pull the connector off, I’m not sure if I could reach in far enough to plug in the new one securely. So any suggestions besides taking it to a garage? I don’t see an obvious way to get to it from the top. Many thanks in advance.

lean code means air leak. not oxygen sensor. you have either a bad upper intake seal or you need the injectors cleaned. but first you have it diagnosed for the leak.

Thank you. I was wondering about that. BTW, P0174 is the only code. There is no misfire and the engine idles smoothly just below 7,500 rpm. I have been consistently using Costco 91 octane for almost 2 years, haven't had any problem. I assume the ethanol in the Costco gas would keep the injectors clean. Should I take it to my local garage (with experience working on rovers) to check for air leak or is this something I could do myself?

have them check it. you could easily do it wrong an replace the wrong part.

I wish we could get rid of the damn ethanol :(

My local garage believe they see more "failed" oxygen sensors now due to being coated as a result of the ethanol adulteration. This causes the oxygen sensor to react too slowly for the ECU so it flags a code and you end up replacing your expensive oxygen sensors....

ethanol is causing carbon deposits on the valves and the injectors. not so much oxygen sensors. That is mostly from reprograms that are needed.

Wish I could change the title of this thread to "It's not the oxygen senor" :) Now I've got P0171 along with P0174, so it's either an air leak or the MAF sensor. So far I've put fuel system cleaner into the gas tank and pretty much used up the tank. And I found non-oxygenated (ethanol free) gas and filled up.
It's my wife's car that doesn't get driven a lot so we drove through the mountains over the weekend to see the colorful leaves and to use up the gas. It drove fine for almost 200 miles up and down the mountains and on the freeways.
Should I try cleaning the MAF sensor before taking it in?

You beat me to it! I was just going to post that a lack of P0174 doesn't indicate a lean mixture on just one bank. The fuel trims have to be past a threshold for "x" time period. If Bank 1 is 18% and Bank 2 is 15%, both banks are lean, but only a P0171 will set.

So now that you know both banks are lean, look for common issues: MAF sensor, loose intake ducting, low fuel pressure, etc...

You could try cleaning the MAF sensor, but I have had very little success cleaning these as opposed to some other styles.

If it has recently had coil/plug wires done, it could be that the intake gasket was re-used or didn't get seated fully.

The MAF sensor is definitely dirty, the side facing the air box is covered with grime. Cleaned it with CRC Mass air flow sensor cleaner. Drove around for about 15 minutes at speed up to 60mph but the CEL is still on. So what would it take for the codes to clear on their own? Or at which point should I replace the MAF sensor or take it in to check for air leak?

It will most likely take a few drive cycles for the light to clear on its own. If you don't have the ability to clear faults or reset fuel adaptations, I would drive it for at least a week before condemning your recent attempt as unsuccessful. Fuel adaptations need time to "re-learn" whats going on and OBD-II needs a few drive cycles of "passing" tests before turning the light off.