Checking for air leakage in the exhaust system: Check

WARNING: This page is about a different car, the 2002 Volvo C70, 2001 Volvo C70, 2000 Volvo C70, 1999 Volvo C70, and 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Checking Exhaust System For Leaks Between Cylinder Head & Rear Heated Oxygen Sensor

Courtesy of VOLVO CARS OF NORTH AMERICA.

Check exhaust system by spraying a soap solution on all joints and connections between cylinder head and rear heated oxygen sensor (HO2S).
Only very small and slow bubbles are permissible.