C0542: Bremsdrucksensor B — Stromkreis niedrig
Was zu tun ist
Your brakes still work — this is the electronics layered on top of them, not the hydraulics. Expect stability control and any automatic braking assistance to be switched off, and the dashboard to say so.
Drive as though the car has no stability control, because it has none: more room in the wet, gentler on cold or greasy roads, no sudden corrections. Nothing feels different until the moment the system would have intervened, which is exactly the trap.
On a hybrid or electric car you may also notice the pedal feels different and the car coasts more freely — that is regenerative braking dropping out and falling back to the friction brakes. Safe, and worth mentioning to whoever looks at it.
Get it seen promptly rather than urgently. Mention any recent brake, suspension or wheel bearing work; these sensors and their wiring are disturbed by all three.
Was dieser Code bedeutet
Brake pressure sensor B is reading low.
A brake pressure sensor is how the car knows how hard you are actually braking, as opposed to how far the pedal has moved — and on a modern car those are different questions.
Stability control, hill hold, automatic emergency braking, brake assist and regenerative blending all read this measurement. It tells the system the real hydraulic effort in the circuit, which is what separates a firm stop from a panic stop and what lets the car decide when to intervene.
So the failure is rarely felt and frequently consequential. Ordinary braking is hydraulic and mechanical: it works with the sensor dead. What stops working is everything clever built on top — and the car will usually say so by switching stability control off and lighting the dashboard.
On a hybrid or electric car there is a further consequence. Regenerative braking blends motor braking with friction braking, and the blend depends on knowing the driver's actual demand. A car that has lost that measurement falls back to friction braking, which is safe, less efficient, and often noticeable as a change in pedal feel.
A constant low usually means a short to ground or a lost supply — the signal is pinned at the bottom of its range regardless of what the hydraulics are doing, so the module knows immediately that it is being told nothing.
Because a rail fault presents identically to a sensor fault, the cheap check comes first: inspect the connector before condemning the part. These sensors thread into the hydraulic unit in the engine bay, where heat, salt spray and washing all reach them.
Why this page exists when its neighbours do not. Nothing in the public web documents this block — four independent searches established that on 2026-08-10. This code is written because a manufacturer named it, with its definition, in a technical service bulletin filed with the US road safety regulator, and that OEM wording agrees with the standard's own enumeration. Its neighbours have no such document, so they remain undocumented rather than guessed.
Wahrscheinliche Ursachen
Hier anfangen
- Korrodierter oder loser Stecker · einfach
- Drucksensor des Bremskraftverstärkers defekt · Fachwerkstatt
Seltener
- Leitung mit Masse kurzgeschlossen · Fachwerkstatt
- Kabelbaum beschädigt · mittel
Symptome
Beteiligte Bauteile
Information, keine Handlungsanweisung
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