Part numbers: Walker 25025109 (upstream), 250241138 (downstream), 250241140(mid)

I recently started noticing a bit of roughness at idle, poor fuel mileage and an intermittent O2 sensor heater circuit bank 1 sensor 1 DTC, so it was time to renew the oxygen (O2) sensors.
My 2013 XJL Supersport has ticked just over 100K miles and I am unfortunately out of the extended O2 sensor warranty that Jaguar offered due to the premature failure rates of the OE Bosch sensors.

The AJ133 V8 has six oxygen sensors, three on each bank of cylinders- upstream, downstream, and also in the center of the catalyst. The widely accepted service life of oxygen sensors is around 100K miles and common failure symptoms include slightly rough fueling, poor gas mileage, and an associated DTC. Replacement of all six of these sensors at a dealer or independent shop costs upwards of $1500, so it's time to DIY. I haven't noticed many X351 or Range Rover owners doing this service themselves, and they have my empathy. These sensors tend to seize up in their threaded bungs due to the intense heat cycling of the exhaust system, and removal is quite tedious with low visibility.



The aftermarket will sell you a curved O2 sensor tool or a cast iron tool. I own both tools, but the upstream O2 sensors gave me problems. The curved tool did not give me enough leverage to crack them loose, and the cast iron tool was too short to engage around the wide exhaust pipe. I took the cast tool to my shop and modified it to increase the offset, and fabricated another small ⅜" offset socket to keep the axis of rotation of my socket wrench centered about the sensor. Centering the axis of rotation of the tool prevents too much off-axis load on the hex head of the sensor, which could strip and cause more difficulty.


Homemade tools!

Here's the tool in situ:



As you can see, access to the upstream sensors on the V8 is completely blind. After soaking in penetrant overnight, my homemade tool cracked both of them loose and I was able to replace all six sensors and clear the DTC in SDD. My Jaaag is back to running smoothly for less than $500, and we will see what fuel mileage improvements I get.