I have tripped over my confusion as to what is the correct upstream O2 sensor for my 2006 XKR. Looking at "reputable" manufacturers, I went to densoautoparts.com and boschautoparts.com and found the following model-year part number patterns. (Though I was focused on the XKR, it looks like the XK/XK8 specs were the same as the XKR's.)

2002 (last year of the 4.0L): Denso 234-9016 and Bosch 15627 - (2003 brought forth the 4.2L)
2003-2005: Denso 234-9029 and Bosch 15627 - (Denso part number changes, Bosch remains the same)
2006: Denso 234-9125 and Bosch 15627 (last of the X100 - Denso part number changes, Bosch remains the same)
2007-2009: Denso 234-9125 and Bosch 15375 (the X150 starts - Denso part number remains the same, Bosch changes)
2010: the 5.0L starts

So what happened in 2006? Whom to believe? Denso or Bosch? Did Denso jump the gun? Was Bosch asleep at the switch? Does the difference even matter?

 

wire length thats’s it

all the cup air fuel sensors are the same. denso only

 

Get the genuine Denso sensor. Anything else is much more likely to cause problems....

 

I need a bit of schooling on O2 sensors. I think I understand the significance of the Upstream sensor - it ensures that the correct air/fuel ratio enters the catalytic converter so the catalyst can do its job, so it provides a feedback control loop to the ECM. But the Downstream sensor is at the outlet of the catalytic converter (and is much the cheaper of the two sensors). So is the function of the Downstream sensor merely to flag issues with the catalytic converter, or does it also provide some level of feedback control?

 

downstream is used for fine control and also cat monitoring. the strategies are pretty complicated

 

This post caught my eye, can't help so much on the part numbers (but definitely buy denso) but do want to guide you to the screenshots I put in this post which may help you when it comes to getting the old sensors out... https://www.jaguarforums.com/forum/x...d-dtcs-276088/

For the connectors, I advise attaching string to the o2 sensor or connector when you pull it out to create a fish line you can use to route the new wire/connector into place. Cos the connectors themselves behind the engine are a #$%^ to reach. Especially the drivers side one.

 

The Jaguar X100 uses a Denso engine management system and as far as I can recall all of the original sensors are made by Denso.

I have found that Denso's parts finder for Europe is more accurate for Jaguars than the U.S. parts finder:

Denso Parts Finder Europe

Cheers,

Don

 

I did get the Denso 234-9125 Air/Fuel Sensor (aka O2 Sensor) for my 2006 XKR to replace the Bank 2 Upstream (aka Upper) O2 sensor. It fit perfectly and fixed the P1627 DTC. Way back at the beginning of this thread, @xalty stated that the Denso O2 sensors were the same functionally, except for differing cable lengths. He was exactly right. The 234-9125 has a cable length of 11.89", which was what I needed. The 234-9029 specified for the pre-2006 4.2 X100 (which confused me) has a cable length of 17.72", significantly longer. For some reason, the US 2006 X100 O2 sensor cabling geometry at the rear of the engine seems to be simpler than the pre-2006 4.2 liter X100s. Perhaps this MY2006 was anticipating the revised 4.2 liter cabling in the upcoming MY2007 X150? All's well that ends well.

PS. I did find the best prices were at RockAuto.