Code
P0557
Generic
P — Powertrain
Brake Booster Pressure Sensor Circuit Low
Views:
UK: 12
EN: 14
RU: 10
AI status
Completed
Completed
100%
Causes
- Short to ground in sensor signal wire
- Open or corroded connector or wiring (including chafing)
- Failed brake booster pressure/vacuum sensor
- Loss of vacuum supply (leaking vacuum hose, failed vacuum pump, or intake leak)
- Faulty ABS/PCM input or internal module fault
- Incorrectly installed or aftermarket components
Symptoms
- Brake warning light and/or ABS/ESC warning illuminated
- Increased brake pedal effort (reduced power assist)
- Harsher brake pedal feel or longer stopping distances
- Reduced engine vacuum (hissing noise) if vacuum leak present
- Stored DTC(s) and possible limp or reduced-function modes
What to check
- Read freeze frame and related codes with a scan tool; capture live data for brake booster pressure/vacuum sensor
- Visual inspection of sensor, connector, and wiring for damage, corrosion, or water intrusion
- Wiggle test while monitoring live data to look for intermittent changes
- Check vacuum lines, check valve, and vacuum pump (if equipped) for leaks or failures
- Backprobe sensor connector to measure reference voltage, signal voltage, and ground
- Measure continuity to ground for the signal wire to check for shorts
Signal parameters
- Most systems use a 5 V reference and return a signal typically in the 0.5–4.5 V range
- P0557 usually indicates signal much lower than expected (for example
- Reference voltage should be ~5 V (key ON), ground should be near 0 V
- Resistance to ground on signal wire should not be low (avoids short-to-ground)
- Vacuum vs signal: applying vacuum should change the sensor voltage smoothly (refer to factory spec)
Diagnostic algorithm
- Retrieve and record all related codes and live data. Note freeze-frame conditions.
- Perform a visual inspection of the sensor, connector, and wiring harness for damage, corrosion, rodent chewing, or water intrusion.
- With ignition ON (engine OFF), backprobe the sensor: verify 5 V reference (if used), good ground, and signal voltage. If reference or ground missing, repair supply/ground first.
- If reference and ground are present but signal is low (~0 V), disconnect the sensor and measure signal pin continuity to ground; a short to ground will show low resistance—repair wiring.
- If wiring checks out, reconnect sensor and apply vacuum (or run vacuum pump) while monitoring live signal. If signal does not change per spec, replace sensor.
- If signal is intermittent during wiggle test, repair/replace wiring or connector as needed.
- If wiring and sensor test OK, check vacuum source (vacuum pump, check valve, intake manifold) and repair any leaks that could affect sensor readings.
- If all external checks pass, consider control module input fault—perform module diagnostics or consult manufacturer procedure before replacing the module.
- After repairs, clear codes and perform road test or reproduce conditions to confirm the fault does not return.
Likely causes
- Damaged or disconnected sensor connector/wiring
- Sensor shorted to ground
- Failed brake booster pressure/vacuum sensor
- Vacuum hose leak or failed vacuum pump reducing sensor input
- Control module input circuit fault (less common)
Fault status
Status
DTC P0557 — Brake Booster Pressure Sensor Circuit Low. The control module detected a low/near-zero signal on the brake booster pressure (vacuum) sensor circuit. Possible causes include a short to ground, open/corroded connector, failed sensor, or loss of vacuum supply. Verify wiring, sensor, and vacuum source before replacing modules.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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