I've copied my post from another forum so apologies if the phrasing seems a bit odd -

My XJR still doing it's occasional 'No DSC, No ABS, Trac not available' followed by 'Engine Failsafe Mode' trick to annoy me. Normally between 8-12miles into a trip.

When it started doing it very occasionally it didn't log any codes my ODBII reader could see. But now it's started logging P1646 & P1121. I've not googled the latter yet, but the first one appears to refer to the upper O2 sensor on bank one. So a faulty lamba, that'd explain the fuel code too I bet. It'd also explain the failsafe mode which restricts the engine to just under 2,000rpm & stops it responding to the throttle.

I'll do a bit more googling etc to confirm it & see if there is way to test the sensor, I've seen something about 5Ohm across grey wires but that referred to an S-type so might not apply.

Can you tell me if I've got the correct answer for what the code refers too? If so bank one is the RH side as sat in the car correct?
Can I test the sensor or is it just a case of replacing it & seeing what happens?