You do not say why you have removed the sensors, but presumably because you think they are faulty. I have submissions on this forum concerning exhaust emissions on bank 1 (left bank) and associated catalytic converter problems, that I experienced and cured on my S-Type. If you suspect the sensor (Upstream or downstream) your first step should be to read any codes that are entered, via your OBD 11 connection. Usual you get Yellow Management Light on clock and when read is usually, depending on which Bank of cylinders is at fault, a Code P0240 or P0230.
If the sensors or sensor are/is faulty your best long term fix is to replace them with new. Whatever you do make certain they are a good make, preferably OE specification and at avoid the cheap Chinese products that are offered on the likes of Ebay etc.
Good Luck and Best Wishes, Regards, John