P3604high severityPowertrain
Start-Stop Brake Vacuum Pump Performance
on 2010 Subaru Outback 2.5L H4 · AWD
What this code means
The electric brake vacuum pump that maintains brake boost during engine-off periods in start-stop systems is not providing adequate vacuum.
Symptoms
- Start-stop disabled
- Firm brake pedal during engine stop
- Brake assist warning
- Start-stop inhibited due to brake system
- Hard pedal after one or two stops
Common causes
- Electric vacuum pump motor weak
- Check valve in vacuum line leaking
- Vacuum line crack or disconnect
- Pump control module fault
- Brake booster diaphragm leak
Diagnostic steps
- Monitor brake vacuum level during engine-off events
- Test electric vacuum pump operation
- Check vacuum lines and check valves
- Measure vacuum decay rate with engine off
- Test brake booster for leaks
Repair notes
Replace electric vacuum pump or check valve. Repair vacuum line leaks. Ensure brake boost is adequate during engine-off periods.
Other Powertrain codes on this vehicle
P0001
Fuel Volume Regulator Control Circuit/Open
P0002
Fuel Volume Regulator Control Circuit Range/Performance
P0003
Fuel Volume Regulator Control Circuit Low
P0004
Fuel Volume Regulator Control Circuit High
P0010
Intake Camshaft Position Actuator Circuit/Open Bank 1
P0011
Intake Camshaft Position Timing Over-Advanced Bank 1
P0012
Intake Camshaft Position Timing Over-Retarded Bank 1
P0013
Exhaust Camshaft Position Actuator Circuit/Open Bank 1
P0014
Exhaust Camshaft Position Timing Over-Advanced Bank 1
P0015
Exhaust Camshaft Position Timing Over-Retarded Bank 1