Ijust bought a 2004 S40 for my daughter. It has 35,000 miles on it. I have noticed that when I first start the car and just move it about a cars length, the brakes are not working properly. They feel like the old standard brakes, with no power assist. You really have to stand on the brake pedal to get the car to stop. It feels like the power brakesare not working. Most "power" brakes work off a vaccum assist, but it acts like there is no vaccum. However, by the time I leave the driveway, everything is OK. I'm not sure if it is the vaccum assist not working, the anti-lock circut not working, or if it is a normal thing. I read in the manual that the car has to get to 4 mph and theABS does a self-test. So, if I move the car a little in the driveway, forward or backwards, the brakes are hard and you have to push on the pedal as hard as you can.I checked the vaccum pump. I disconnected the pump's electrical connection and applied 12V from the battery. The pump ran making that humming/buzzing soundeveryone mentions. Also, when I took the power away from the pump, I could hear the backflow valve click. I then took out the relay and check it with a meter and voltage and it is working. I also checked the fuse, and it is also good.For some reason, the circut to the vacuum pump is not completing and the pump is not coming on.
Any ideas?du907

 

I have a 2000 S40 and I had nearly identical symptoms with mine until the dealer told me there was a service recall bulletin on the power assist brake pump. They fixed it on their dime of course, but the symptoms were identical to yours. It can be quite frightening when you just start the car and nearly back into someone.
I feel your pain and worry!

Good Luck!

 

the volvo has an abs startup, after reaching about 5-10 mph it automatically will check for the brake system...once you have used the brakes a couple times you shouldnt have this problem, its only when starting up, i have the same thing...

 

I've seen that all the time.... The vacuum activated switch connected before your vacuum pump (supply brake booster with vacuum) is cracked or broken causing water flows into the pump and burn the pump out. If u see the switch broken (cracked and spring popped out) replace both the vacuum pump and switch all together. There in nothing to do with the self check... The self check for the brake system is only for the ABS and DSA (if equipped) system.. It does not do mechanical or hydraulic system check in the brake system if a mechanical fault or physically part get broken it cannot tell! The brake warning light ((!)) is only for brake fluid level and the brake light for the ((p)) is for parking brakes still applied...

 

Is this the same problem?
https://volvoforums.com/m_115594/tm.htm