Two problems related to air bag not deploy have been reported for the 2004 Volvo S40. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2004 Volvo S40 based on all problems reported for the 2004 S40.
On October 4th I was involved in a car accident in which a driver hit my car on the driver's side pushing my car down a pth in the woods in fairfax, va. My airbags did not deploy although the sensors were activated according to the collision center.
During a frontal drivers side crash the drivers side airbag did not deploy causing injury to the driver. However the passenger side airbag did deploy, but no passengers were present at the time of the accident. The impact of the crash was mostly drivers side. I also believe the braking system failed since my car failed to slow like a car should during braking.