Air leaks in the intake system, checking (B5204T5; B5254T4; 2005-2007): Removal: Check

Fig 1: Identifying Gentle Hissing Sound Heard From Oil Filler Opening

Courtesy of VOLVO CARS OF NORTH AMERICA.

Remove the oil filler cap. Connect the compressed air hose. Adjust the regulator to obtain a maximum pressure of 0.3 bar  .

There may be a gentle hissing sound from the oil filler opening. This is due to the opening of an intake valve and the leakage of cylinder pressure past the piston rings. If a leak is suspected, spray a soap solution onto the area. Remedy any leakage.