I've been getting code P1647 "Heated Oxygen Sensor Control Module, Bank 2 Open / Shorted." All four of my O2 sensors were replaced about one year ago when I also replaced my catalytic converters. I believe the sensor is the upstream sensor on the right side (passenger side in the USA) exhaust. I unplugged the sensor and reconnected it. It had fresh looking dielectric grease on the contacts. After doing some reading here on this thread it seems I should check the relay. After looking at a wiring diagram I found this illustration that indicates the relay I'm after is in the Control Module Enclosure.
My question is: How problematic is it to open this box and get to the relay? Is it worth it for me to try this myself of do I run the risk of causing more issues. Judging by videos online I will have to fully unplug and remove the entire Control Module. Is there a trick to doing this?


Relay Location

 

From memory, bank 2 is driver side in the US.

Dielectric grease is supposed to be used in places like rubber boots around spark plugs for its ability to enhance electric isolation, not conductivity. It should certainly not be inside electrical connectors.

The "enclosure" is the basic sheet metal bin. I once looked into the location of these relays, and realized at the time their location was poorly documented. Maybe take that picture above and compare it with your actual engine bay. From memory, they are at the edge of the other bin instead.

 

Thanks fmertz. Your relay was very helpful. Some trial and error determined that you are indeed correct that the Bank 2 O2 sensors are on the driver's side and not the passenger side as I originally thought. Thanks for pointing that out. Not sure what dielectric grease is good for or when to use it. It was put there by someone I know to be a good mechanic with a lifetime of professional experience, but based on what you said I decided to try and clean the connector contacts off. I used QD Electronic Cleaner and then dried with compressed air. Alas this didn't prevent the code from registering.

Having tried that I went looking for the relay. I found out that you don't need to open the control module enclosure to find the relays. They sit outside the module enclosure but inside the bin which encloses the module enclosure near the windshield in the passenger side corner and covered by the hand removable panel. In my 2004 XK8 there were two banks of relays covered by hand removable covers. With the "XK Range 2003 Model Year Electrical Guide" pdf on page 43 I used the "Engine Management Switched Power Distribution" diagram to find that the relay I was looking for had white/blue, yellow/red, brown/green, and black wires connecting to it. This allowed me to ID the right relay.
Here is a picture with all the covers removed. The Bank 2 O2S heater relay is marked with a the red arrow.


As you can see the fuse box and Module enclosure do not need to be involved to access the relays. I also found other relays on the matching drivers side compartment but none had matching wire colors. So I removed the relay and started the car and got the P1647, but also got P0057 "HO2S Heater Control Circuit Low (Bank 2 Sensor 2)." This told me I had the right relay. I took the relay apart to check for signs of wear but it looked good as far as I could tell:

I tried to take it apart more but it would have to be broken in the process so I stopped. It is interesting to note that this relay looks like a much more substantial device than ones I had seen on other threads.
So I put it back together, and plugged it back in, and started the car. The P0057 code went away but the P1647 remained. So it seems the relay is not the problem.

When reading about code P0057 this page suggested putting an ohm meter on the heater coil of the O2 sensor. At the O2 sensor connector I put an ohm meter on the heater coil. The heater coil wires were identified by finding the two fatter wires going into the connector from the wiring harness. The meter registered infinite resistance. For comparison I checked the Bank 1 (passenger's side) sensor and got 1.6 ohms. So based on the readings it looks like I need to replace the O2 sensor. I will try that and report back.

 

Hopefully last update: Replaced the Upstream drivers side (USA) O2 Sensor and it seems the issue is fixed. If I had to do it all over again, I would have checked the resistance on the O2 Sensor first thing. The new one had 0.8 ohms resistance, the matching passenger side one had 1.6 ohms. So they vary. But they should not be infinite or zero. The heater coil pins are the only ones I got to register any resistance. From memory here is a pic showing the location of the heater coil pins on the sensor side connector: