2003 Chevrolet Suburban • 48,000 miles

Display says to sevice brake booster

In vacuum assist brakes there is a motor mounted on the booster. When I start the truck the elec motor turns on and runs for about 1 mim then shuts off. My display in the dash says to service brake booster I check the wires and the blue that pluge into the elec motor says 12 + volts when I start the truck but when the elec motor on the booster turns on the volts drop to 4+ in 1 minute the elec motor shuts off and the volts jump from 4+ to 12+ back and forth. What do I need to do?I tried following: disconect battary to clear codes, did not workcycle the key off and on 5 times, did not workread codes Nonechecked fuses, okchecked the alternator, ok
April 8, 2012.

If the voltage went to 4 volts with it on, there is a ground issue./ It should be 0 volts.

The pump motor may be bad or the main ground for the motor may be bad.


Thank you for helping out!
If I unplug the connector from the motor and check the blue wire while the truck is running it reads 12v + When I plug it back into the motor, in 10 sec the motor will turn on and when I check the blue wire that s when it goes up and down between 4v to 9v to 12v back to 4v over and over.
Are you saying the blue wire should read 0v when the truck is running? Or should it be at 12v
if it is the motor, can I get that only? Do you know where I can get one, and what is the motor called?
When I look up the brake booster I don t see the little motor that the vacuum line plugs into
I also checked and cleaned the ground wire under the driver s door still does the same thing

Apr 9, 2012.
It is a hyravac system. Most likely a dealer item and very expensive.
I would have a shop verify this for you before throwing anything at it.

The measurements I mentioned were on the ground side.