To all present and former Jaguar Forums contributors...thanks again!

Had a new code for me, P1646. Being a manufacturer specific code, my cheapo scanner identified it as 'Auxiliary Device'. Uh, thanks, scanner.

Looking it up online, I find 'Right Bank, Upper O2 sensor'.

Having had experience extracting 20+ yr old lambda sensors located close to the engine, my thoughts were not "Yipee!".

But I KEPT looking it up on older Jaguar Forum threads, and was warned these man-specific DTC codes are frequently year, VIN and aspiration-specific.
So pulled the Jaguar data so thoughtfully supplied by JF contributors. There it was!

2001 XJR's P1646 is the secondary fuel pump relay coil. Nowhere near an O2 sensor. Much time saved, and a quick fix.

Thanks again to contemporary and earlier contributors, who make it possible for us shade-tree mechanic bottom 95%ers to drive around in grace & style!

 

Yes, this is a great site for info provided by those who have come across these issues before us, glad you got it taken care of.
This is from Jag-lover.org and state they don't guarantee the overall accuracy of it...
The first alpha character identifies the system generating the code

• P = Powertrain
• B = Body
• C = Chassis
• U = Undefined
  
  The second digit says if the code is generic - same for all OBD-II systems - or manufacturer specific
• 0 = Generic (zero)
• 1 = Enhanced (manufacturer specific)
  
  The third digit is sub-system type for that code
• 1 = Emission Management (Fuel or Air)
• 2 = Injector Circuit (Fuel or Air)
• 3 = Ignition or Misfire
• 4 = Emission Control
• 5 = Vehicle Speed & Idle Control
• 6 = Computer & Output Circuit
• 7 = Transmission
• 8 = Transmission
• 9 = Reserved
• 0 = Reserved

Well, if you do come across the need to replace any of the O2's, here's my write up. It's not as bad as you think...it even has pictures.

https://www.jaguarforums.com/forum/x...cement-195018/