P0556 Brake booster pressure sensor circuit range or performance

Brake booster vacuum sensor reading out of range

P0556 in short

P0556 means the engine computer got a brake booster pressure sensor reading outside the expected range. That sensor watches the vacuum that powers brake assist. Causes include a vacuum leak, a failing engine-driven vacuum pump, or a bad sensor or wiring. Get it checked promptly, and stop driving if the pedal turns hard.

Power brakes use engine vacuum, or a separate vacuum pump on many turbocharged engines, to cut the effort needed at the pedal. A sensor on the booster or its vacuum line reports that vacuum, and P0556 sets when its signal does not fit what the engine computer expects.

The fault can be electrical (sensor, connector or wiring) or real (a vacuum leak or a pump that no longer makes enough vacuum). Owners of GM 1.5L turbo cars such as the Malibu and Terrain report P0556 with a hard pedal and a failed vacuum pump, sometimes with camshaft codes when the broken pump damaged the camshaft drive.

Because brake assist is involved, this page explains the fault but does not give do-it-yourself repair steps.

Most likely causes

  1. Failed engine-driven brake vacuum pump (GM 1.5L turbo)

    Supported by vehicle data
    Why it ranks here
    Several NHTSA complaints on the Malibu and Terrain describe P0556, a hard pedal and a dealer or mechanic finding a failed vacuum pump, in some cases with P0014 or P0017 and damage to the camshaft drive. No GM bulletin naming P0556 was read.
    What would change this
    Rises on GM 1.5L turbo engines, especially with P0014 or P0017 or a hard pedal. Falls if booster vacuum measures normal.

  2. Leaking, cracked or misrouted booster vacuum hose

    Common general cause
    Why it ranks here
    A leak in the vacuum line lowers booster vacuum and is a standard cause. GM bulletin 21-NA-045 replaces a misrouted booster vacuum pipe on the Malibu and Impala; its summary does not name P0556, so treat it as context.
    What would change this
    Rises if a hiss is heard or the hose is cracked or loose.
    How to test the vacuum hoses and intake leaks

  3. Faulty booster pressure sensor, connector or wiring

    Common general cause
    Why it ranks here
    The code describes the sensor signal, so the sensor and its circuit are a direct cause.
    What would change this
    Rises if real booster vacuum is normal but the sensor reading is wrong.

  4. Faulty brake booster

    Possible — needs testing
    Why it ranks here
    A leaking booster diaphragm also lowers vacuum; listed as a less common cause.
    What would change this
    Rises if vacuum holds with the booster disconnected but drops with it connected.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Note how the brake pedal feels with the engine running and read all stored codes.

    Low riskTool: scan tool

  2. Have a shop measure booster vacuum with a gauge, compare it with the sensor reading, and inspect the hoses, check valve, pump and wiring.

    Best left to a shopTool: vacuum gauge, scan tool

    Warning:This is brake work. Don't drive with low brake assist; leave diagnosis and repair to a professional.

Symptoms

  • Check engine light or brake warning message
  • Hard or stiff brake pedal, more effort to stop Gets more serious: stop and have it checked.
  • Engine noise, burning smell or reduced power with camshaft codes (GM 1.5L turbo) Gets more serious: stop and have it checked.

How to fix

This is a safety-critical system, so we explain the code but don't give repair steps. Have it inspected by a qualified technician.

Parts and cost context

  • Vacuum hoses and intake leaks:A cracked or loose vacuum hose is the cheapest thing to rule out. On GM 1.5L turbo engines a failed vacuum pump may also mean camshaft and timing parts; get a full diagnosis and quote before approving work.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Chevrolet

  • 2017–2019 · Malibu

    Supported by vehicle data

    Owners report P0556 with a hard brake pedal, and a failed brake vacuum pump found by a mechanic or dealer, once with camshaft codes and engine damage. GM's booster vacuum pipe bulletin 21-NA-045 may also be worth asking about; its summary does not name P0556.

GMC

  • 2020 · Terrain

    Supported by vehicle data

    Owners report loss of brake assist with P0556, sometimes with P0014 and P0017; a dealer recommended a vacuum pump, exhaust camshaft and timing parts.

Ford

  • 2017 · F-150

    Possible — needs testing

    An owner reports a stiff pedal and a Check Brake System message with P0555 and P0556. Single report.

  • P0017Crankshaft and exhaust camshaft positions do not agree (bank 1, sensor B)

    Shares causes Supported by vehicle data

    On GM 1.5L turbo engines, owners report P0556 with P0017 when a failed vacuum pump damaged the exhaust camshaft drive.

  • P0014Exhaust camshaft timing ahead of target or slow to respond (bank 1)

    Shares causes Supported by vehicle data

    Owners of GM 1.5L turbo cars report P0014 with P0556 after a vacuum pump failure.

All Vehicle speed, idle control and engine electrical codes

P0556 questions

Is it safe to drive with P0556?

Only gently to a shop if the brake pedal feels normal. If the pedal is hard or the car needs more effort to stop, don't drive; have it towed.

Sources and review

  1. Kelley Blue Book: P0556 Brake Booster Pressure Sensor Circuit Range/Performance — Kelley Blue Book
  2. TAT Scandata: P0556 Brake Booster Pressure Sensor Signal Out of Range — Technical Assistance Team (TAT), Australia
  3. NHTSA complaint ODI 11496472: 2019 Chevrolet Malibu, hard brake pedal with P0556, vacuum pump — NHTSA Office of Defects Investigation (complaint flat file) ,
  4. NHTSA complaint ODI 11766529: 2020 GMC Terrain, loss of brake assist with P0556 — NHTSA Office of Defects Investigation (complaint flat file) ,
  5. NHTSA complaint ODI 11471869: 2017 Chevrolet Malibu, stiff brake pedal with P0556 — NHTSA Office of Defects Investigation (complaint flat file) ,
  6. NHTSA complaint ODI 11659123: 2019 Chevrolet Malibu, brakes not responding with P0014, P0017, P0556 — NHTSA Office of Defects Investigation (complaint flat file) ,
  7. NHTSA complaint ODI 11757862: 2020 GMC Terrain, burning smell, reduced power, hard pedal with P0556/P0014/P0017 — NHTSA Office of Defects Investigation (complaint flat file) ,
  8. Chevy Equinox Forum: Vacuum pump broke (2018 Equinox 1.5L) — chevyequinoxforum.com
  9. GM 21-NA-045: Impala/Malibu power brake booster vacuum pipe replacement — General Motors / NHTSA ,
  10. NHTSA complaint ODI 11584044: 2017 Ford F-150, stiff pedal with P0555 and P0556 — NHTSA Office of Defects Investigation (complaint flat file) ,
Last reviewed
Written by
Saurabh K.
Editorial review
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