P0571

P0571 sets when the PCM detects an implausible signal pattern from the primary brake switch (the switch on the brake pedal bracket that signals brake-light activation to the PCM, BCM, and cruise-control module). Modern systems use two redundant switches; P0571 typically triggers when the two disagree, or when the primary switch fails to change state during conditions where braking is inferred (deceleration plus throttle closed). Cheapest-first: with key on, engine off, push the brake pedal and watch the brake switch PID on a scan tool. It should toggle cleanly from inactive to active within the first half-inch of pedal travel. If the PID is stuck on (brake-applied with pedal up), the switch is misadjusted, the brake pedal bumper has crumbled (very common on Hondas), or the switch internals are stuck. If the PID never activates, check the brake light fuse and bulbs first; a blown fuse from a stuck-on switch is the underlying cause as often as switch failure itself. Expensive misdiagnosis: chasing transmission shift-quality or cruise-control codes that all stem from a $25 brake switch.

Vehicle-specific patterns: 2007-2014 Chevrolet Silverado, GMC Sierra, Tahoe, Suburban, and Yukon are the GM-wide poster child for brake switch failure; the switch's internal contacts pit and the cruise control drops out before P0571 sets. 2003-2007 Honda Accord and 2003-2011 Honda Element have the famous TSB for the brake pedal rubber bumper (the small rubber stopper the switch plunger rides on) crumbling and falling out, leaving the switch perpetually closed; the $3 bumper grommet is the fix. 2004-2008 Ford F-150 develops a corroded brake-switch connector under the dash that intermittently opens the circuit during humid weather. 2005-2010 Dodge Ram 1500 and 2500 has the brake switch fall out of adjustment after pedal bracket flex, especially after towing. Estimated repair: $30 to $260.