Hi,
I just read the issues of the previous Land Rover owner and I am in the same boat but with a twist. I think we are being taken, but I hope I am incorrect. Yes, we started with the Coolant Leak, thereafter Head Casket was just replaced (we were told it needed to be done to stop the Coolant Leak) and we have now adopted these various ‘Check Service Engine Issues’ which my mechanic has been very good in troubleshooting each and every one of these error codes. Now the twist is we just picked up the vehicle on Friday, with the ‘Service Engine’ lite up (again this wasn’t the initial issue we went it with a Coolant Leak turned into replace Casket issue), was told it will lite up and go away, but if it doesn’t to bring it back after the July 4th holiday, also when using the AC (which now shows 24c vs. Fahrenheits, know idea how they did that, must be after changing the Casket?) the car rattles/shakes, a bit worrisome as one would say. So I just gave them back my vehicle and just got a lovely phone call that ‘Service Engine’ is now showing an ‘OXYGEN’ issue, which I was told would effect my Gas Mileage, is that correct? So now I am being told that I need to change these OXYGEN things which now will cost me an additioanl $700.00 on top of my initial finding out that I have a Coolant Leak ($1,500) & Replacing the Casket (2,019). So am I being had here? What’s the deal? I was bluntly told perhaps it is time to sale the car, wow… I forgot to tell you that the mechanic shop also owns a car dealership shop, so again, are they messing around with this fantastic Luxury Vehicle or what. Please tell me what to do. I am think it is time to get a second opinion?? Worried Land Rover 2004 Owner…
It’s very hard to tell exactly what you’re asking, but I’ll try:
an “oxygen issue” is probably a bad oxygen sensor. I think $700 is an insane price for an oxygen sensor, but then this is a Land Rover, and they’re famous for being unreliable and expensive to fix. It is, after all, British 
I don’t know why they told you that the service engine light would just go away on its own. That sounds to me more like they were trying to kick you out the door so they could start their July 4 holiday earlier.
I would certainly take it to a different mechanic.
I would also consider selling the car, because if you’re balking at the cost to repair it, it’s probably not the vehicle for you. Land Rovers are relatively uncommon compared to more mainstream brands. And they’re not reliable. And it costs a fortune to fix them. People buying Land Rovers should be aware of that up front and be willing to pay for it. Otherwise, there are a good number of equally (and moreso) luxurious SUV’s out there that are much more reliable.
If you have invested $3500 already, then replacing the oxygen sensor(s) makes sense. Note that Bosch makes an exact fit replacement for around $82 each. You may want to have the oxygen sensor work done by an independent mechanic. You might get the sensor replaced for about half of the $700 estimate.
At some point, the best advice might be to sell this car, but given your current investment in the repairs, you need to get more miles out of it.