P0556 Generic (SAE) Basic entry

Brake Booster Pressure Sensor Circuit Range/Performance

Updated 2026-10-02 · Vehicle speed, idle control & auxiliary inputs

Severity

Medium

Typical repair cost

60 – 500 EUR

System

Powertrain

What it means

P0556 is stored when the Brake Booster Pressure signal is electrically valid but does not make sense compared with other sensors or the expected operating range. The circuit is usually fine; the component or what it measures is out of specification.

This entry is compiled automatically from the standard definition and typical diagnostic practice for this type of fault. A detailed, reviewed article is in preparation.

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Symptoms

Check engine light on
Idle too high, too low or hunting
Stalling when coming to a stop
Speedometer or cruise control not working in some cases

Common causes

Brake Booster Pressure worn, contaminated or out of calibration
Mechanical problem in the system the sensor measures
Air, vacuum or exhaust leak influencing the reading
Wrong or low-quality replacement part
Wiring resistance causing a small voltage offset

How to diagnose

Compare the live Brake Booster Pressure reading with a known-good value or a second sensor at idle and at 2500 rpm
Check for air, vacuum or exhaust leaks that could skew the reading
Inspect the component for contamination and clean it if the design allows
Verify the part number is correct for the engine
Replace the Brake Booster Pressure if the reading remains out of specification

Frequently asked questions

Can I keep driving with P0556?

Usually yes for a short time, but expect reduced performance or higher fuel use. Have it diagnosed within a few days.

Will clearing P0556 fix it?

No. Clearing only erases the stored code; it returns as soon as the monitor runs again unless the cause is repaired.