Diagnostic article Generic OBD-II
P0556: Brake-booster pressure plausibility uses several comparisons
P0556 checks brake-booster pressure range and its relationship to other pressure information.
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Documented application
2009 General Motors diagnostic parameter file 09OBDG02 Engine Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability established.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
P0556 is a plausibility check of brake-booster pressure in the specified GM group 02 application. The source includes low- and high-range checks as well as comparisons with ambient and manifold pressure. A sensor can therefore remain electrically connected while reporting pressure that does not fit the operating context.
Range and correlation are separate evidence
The published range boundaries are 1.5 and 107.5 kPa. Another branch compares booster pressure with ambient pressure. These conditions should not be collapsed into a single statement that the booster has lost vacuum; the code concerns the credibility of the pressure information and its relationships.
The manifold-comparison row lacks an unambiguous comparison operator in the extracted and printed specification. This article does not convert that incomplete row into a service-test limit. The exact vehicle diagnostic procedure remains necessary.
Brake-system implications require proper assessment
A pressure-signal fault does not establish the amount of brake assistance available. If braking effort or assistance has changed, the vehicle needs appropriate professional assessment rather than a driving reassurance based on this code.
Preserve the pressure readings, related airflow or ambient-pressure faults and the monitor's completed status. The source limits this entry to named internal application groups, without proving model fitment. Verification should establish credible pressure relationships and the prescribed brake-system function checks; clearing a diagnostic code alone cannot verify brake assistance.
Source and applicability
2009 General Motors diagnostic parameter file 09OBDG02 Engine Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability established. This explanation describes the documented monitor, not a universal repair procedure.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
Brake Booster Pressure Sensor Circuit Range/Performance
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT