What P0559 means
The brake booster pressure sensor (5 V reference, signal, ground) measures the vacuum in the brake booster.
How the engine computer detects it
On direct-injection, turbo, stop-start and hybrid engines intake vacuum is scarce, so the engine module watches it and creates vacuum when needed – closing the throttle, suppressing engine stop or running an electric vacuum pump. That makes it an input to idle and throttle control. P0559 means the signal jumps briefly – a loose contact or broken wire under movement – without staying out of range long enough for P0557 or P0558. No manufacturer document available to us uses it; GM catches dropouts through the sample counters of P0557/P0558. CARB requires input components to be checked for circuit faults.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Warning comes and goes
- Stop-start inactive at times
- Check engine light (depending on the maker)
Common causes
- Loose contact at the sensor connector (pin tension, corrosion) Most likely
- Broken or chafed wire moving with the engine Possible
- Sensor with internal dropouts Less likely
How to diagnose P0559
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: brake booster pressure sensor, sensor wiring, engine control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 5
- Vehicle speed, idle control and auxiliary inputs
- 59
- Specific fault
Questions drivers ask
Can I drive with code P0559?
Usually yes, carefully. Your hydraulic brakes normally keep working, but ABS, traction and stability control may be off, so the wheels can lock in a hard stop. If the red brake warning light is on, the pedal feels soft or different, or the car takes longer to stop, don't drive: have it towed.
Will P0559 clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
Can I fix P0559 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.