Cause
Faulty brake booster travel sensor
The sensor measuring how far the brake servo's rod has moved, faulty. It tells the module how hard the driver is braking, which matters most on vehicles that blend regenerative and friction braking or that need to judge an emergency application.
A fault withdraws the blending rather than the brakes. On a hybrid or electric vehicle the module falls back to friction braking alone, which is safe and noticeably different to drive — a heavier pedal and no regeneration. Brake assist and autonomous braking also withdraw. The module cross-checks it against the brake switch and the pressure sensor, so a correlation code means they disagree rather than that any one is definitely wrong — and a misadjusted switch produces that with a healthy sensor, which is the cheaper thing to eliminate first.
Typically specialist work. Needs equipment or training most home workshops do not have.
Codes this can cause (1)
Codes where this is a likely explanation first, rather than merely a possible one.
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