P15B3 on 2012-2016 Peugeot 3008 — Brake Fluid Pressure Sensor 'A' Circuit Range/Performance (Honda); Fuel Additive Level Low (Peugeot/Citroën)

P15B3 is an OBD-II diagnostic trouble code meaning “Brake Fluid Pressure Sensor 'A' Circuit Range/Performance (Honda); Fuel Additive Level Low (Peugeot/Citroën).” P15B3 is a manufacturer-specific code, and its meaning depends on the brand of vehicle that set it. On some Honda models — most often hybrids, where the powertrain computer reads brake fluid pressure to coordinate regenerative and hydraulic braking — it indicates the brake fluid pressure sensor 'A' signal is out of its expected range, which can light the check-engine or brake-system warning lamps and may change brake-pedal feel or disable regenerative braking. On Peugeot and Citroën diesels, the same code instead refers to the particulate-filter fuel additive (Eolys) system: the computer has calculated that the additive level is below its minimum threshold, usually because the additive tank is nearly empty. Neither version means you must stop immediately, but a brake-pressure-sensor fault on a Honda deserves prompt diagnosis because it affects the braking system, and ignoring a depleted additive on a PSA diesel eventually prevents proper DPF regeneration and can lead to a clogged, expensive-to-replace particulate filter. Because usage genuinely differs between manufacturers, confirm the definition with a make-specific scan tool before replacing parts. This code is most commonly reported on 2012-2016 Peugeot 3008, with repair costs ranging from $300 to $6,500.