C0054

C0054 is a fault in the brake apply (brake pedal position) switch circuit — the EBCM/ABS module is not seeing a valid signal transition from the brake switch when the pedal is pressed, or is seeing conflicting signals between the primary stop-lamp switch and a secondary brake-position sensor. Modern brake systems often use two independent contacts on a single switch (one for stop lamps, one for ABS/cruise/stability) and a fault on either contact can set this code. Cheapest-first ladder: (1) Pedal-press test with a DMM at the switch connector: with pedal released the ABS/stop signal wire should read 0V (open switch); with pedal depressed it should read battery voltage (12-14V, closed). A switch that reads battery voltage at rest or zero with the pedal pressed is mechanically failed. (2) Visual inspect the stop-lamp bulbs and circuit — a shorted or grounded stop-lamp bulb pulls voltage on the switch circuit and confuses the ABS module; pull the bulb and re-test. (3) Pedal-bumper check — the rubber pedal-stop bumper crumbles to dust over 10+ years and lets the pedal travel a few extra millimeters at rest, which is enough to close the switch slightly and confuse the module; a $4 bumper resolves it. (4) Scan-tool brake-switch state monitor during a slow pedal apply — the switch state should transition cleanly from 'released' to 'applied' within the first 1/2 inch of pedal travel; a switch that bounces between states or doesn't transition until the pedal is half-way down is misadjusted or worn. Expensive-misdiagnosis caveat: replacing the brake master cylinder or booster when the actual problem is the $20 stop-lamp switch — symptoms can overlap with low pedal feel or 'pumping up' the pedal when the real issue is the switch confusing the ABS module into an extended self-test mode.

Vehicle-specific patterns: 2009+ Ford F-150 throws C0054 from a known stop-lamp switch wear issue — the switch is mounted on a pedal-bracket tab and develops contact-bounce around 80k miles; Ford issued service bulletins covering the symptom of stop lamps staying on or cruise/ABS faults setting together. 2007-2010 Toyota Camry/Avalon/Sienna throws C0054 from a similar stop-lamp switch wear pattern that Toyota addressed in TSB territory — the symptom is intermittent stop-lamp operation plus stability-control warning lights, and the $25 switch is a 10-minute under-dash swap. 2004-2009 Cadillac SRX/STS throws C0054 from a failed brake-pedal position sensor (separate from the stop-lamp switch) that lives on the pedal bracket. 2008-2013 Jeep Grand Cherokee throws C0054 from corrosion at the brake-switch connector under the dash where carpet moisture wicks up the harness. Estimated repair: $25 to $250.