Land Rover Repair: 99 Discovery O2 sensors, sensor ot, inspection sticker

Question
Hi there,

I have a 1999 Discovery, which I recently brought into the dealer for the 82,500 mi service.  The check engine light was also on, so I asked them to look into it.  From the paperwork, the codes were:

P0158: O2 circuit high voltage bank 2 sensor 2
and
P1193: H02S header circuit inferred open circuit, downstream sensors

They replaced the downstream sensor(s?).  I went ahead with the repair they recommended becuase my state inspection sticker was about to expire and the service guy said I'd fail.  He was not very nice to me when I simply asked 1) what the part does and why I need it and 2) what exactly they do in the 82,500 mi "emissions" service.  I just like to understand what is happening with the car, and this guy couldn't explain anything.  Worse, he was defensive and kind of rude to me.  So I left a little bitter, but all was well for 2 weeks until the check engine light came on again.  I called the dealer and they  said they would look into it but it would probably cost me unless it turned out to be something faulty with the work they just did.  Now, I think since I just dropped $850 on repairs and the 82,500 mi service they could at least check their work as a courtesy.

So, I did some reasearch, bought an OBDII reader, and checked it myself.  The code that came up is P0138: 02 cicuit high voltage bank 1 sensor 2.

Now, what I want to know is, could that be related/caused by what they did?  If so, I'll take it back to the dealer to have it fixed.  If it's not, I don't want to go back there because I'm not spending another cent at that dealership.  Also, how urgent is this sort of code?  I need to gather some funds before I can afford any more repairs.

Thanks in advance for your help.

Answer
The code you have points to a problem in the other downstream o2 sensor heater - the one the dealer didn't change.  It's not uncommon to have the second fail shortly after the first.

It may be a bad sensor ot the whole thing may be a wiring problem of some kind.  The only thing you could try at home would be to swap the sensor and clear the code and see what happens