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Discussion Starter · #1 ·
Occasionally in the summer my Engine Service Required Light comes on. Dealer stated that it is my Brake Position sensor. So I replaced it but the problem still exists. Sometimes it impacts my ability to use cruise control. Also, I can hear a humming/buzzing for a sec when I take my foot off the brake when the car is not running (year round). I read that is probably my brake booster. Does anyone know for sure before I get too crazy with the booster? Thanks
 

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I've heard a buzzing on both my S60 and S40 when applying the brake when the car is off. Brake boosters normally make a hissing noise when they've gone bad. Start the car and apply the brake pedal as far as it will go, if you hear a loud hissing noise that doesn't stop (It sounds like a vacuum leak), the brake booster is bad.
 

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That buzzing you hear when releasing the brakes with your car off is the brake vacuum pump. As long as it stops after a second or two, it's operating correctly.
 

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Never heard of the brake pedal position sensor triggering a CEL. I've been through a couple of those myself and never threw a CEL.

When the booster leaks you will hear a hissing sound when you depress the pedal. If you are hearing that then you need to replace it.
 

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Discussion Starter · #5 ·
it def is a mechanical buzz and not hiss.

And i look up the code and it states that it is for the accelerator pedal
 

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Not quite sure what you are asking here. A brake booster issue would be exceedingly rare.

It sounds like your brakes are functioning normally. qaz996 is correct. The silver vacuum pump located in front of the battery will run when the engine doesn't supply enough vacuum to the system. If it runs all the time you either have a leak (usually a line, NOT the booster) or the relay has malfunctioned. Early cars (2004-2008) have an updated harness available to relocate the relay & prevent a reoccurrence.

Your real issue sounds like the check engine light. Do you have the actual Volvo code or simply the generic OBD? What year & model are we dealing with?
 

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Discussion Starter · #7 ·
Not quite sure what you are asking here. A brake booster issue would be exceedingly rare.

It sounds like your brakes are functioning normally. qaz996 is correct. The silver vacuum pump located in front of the battery will run when the engine doesn't supply enough vacuum to the system. If it runs all the time you either have a leak (usually a line, NOT the booster) or the relay has malfunctioned. Early cars (2004-2008) have an updated harness available to relocate the relay & prevent a reoccurrence.

Your real issue sounds like the check engine light. Do you have the actual Volvo code or simply the generic OBD? What year & model are we dealing with?
Dealer says:
ECM-941C
Brake Pedal POS sensor to start
0.50 diag fault traced and found brake pedal position sensor is not reading in range it is supposed to.

I replace the sensor myself but that did not correct the issue. I am thinking it is a bad module. What do you guys think?
 
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