WARNING: This page is about a different car, the 2012 Mitsubishi Lancer. However, it is still accessible from the selected car via links, so may be relevant.
Tighten the heated oxygen sensor to the specified torque by using special tool MB991953.
Tightening torque: 44 ± 5 N.m (33 ± 3 ft-lb)
Fig 1: Tightening Heated Oxygen Sensor To Specified Torque By Using Tool