B2740

B2740 is a door-lock switch circuit fault — the BCM is reading an invalid voltage state on one of the lock/unlock switch inputs (typically the driver-door master switch). A properly functioning door-lock switch reads ~5V at rest (pulled up internally by the BCM) and drops to 0V when pressed; B2740 sets when the input is stuck low (shorted to ground), stuck high beyond the pull-up reference, or chattering. Cheapest-first ladder: (1) Operate every lock/unlock button on every door switch while watching the BCM's switch-state PIDs live — a switch that doesn't toggle the BCM's input has either a broken switch contact, a broken wire in the door-jamb boot, or a chafed wire shorted to ground inside the door. (2) Pull the driver-door master switch (usually 2-4 screws and one connector) and bench-test each switch position with a multimeter — should show ~0 ohms pressed, infinite at rest. (3) Inspect the door-jamb wire boot — this is where 80% of door switch wiring failures happen, especially on trucks where the door cycles a million-plus times over a decade. Look for green corrosion, broken strands, and chafed insulation. (4) Replace the door master switch ($40-$150 aftermarket, $150-$400 OEM) only after confirming the wiring is good. Expensive-misdiagnosis caveat: a chafed wire in the door-jamb boot mimics a bad switch perfectly — replacing the switch without fixing the wire just sets the same code in 50 miles.

Vehicle-specific patterns: 2007-2014 Chevrolet Silverado, GMC Sierra, Tahoe, Yukon, Suburban driver-door master switch is the canonical B2740 — the switch's internal contacts wear out from a decade of daily use, and GM replacement switches from the dealer are $200-$400 while aftermarket Dorman units are $40-$80 and last about as long as the original. 2009-2014 Ford F-150 driver-door master switch throws B2740 from the same wear pattern, and additionally from a documented door-jamb wire chafe at the upper hinge boot — fix the wire, not the switch. 2008-2013 Cadillac CTS and 2010-2015 GM full-size SUVs throw B2740 from water intrusion into the door-mounted switch assembly when the door's outer weatherstrip degrades — drying and contact-cleaning the switch sometimes recovers it. 2003-2008 Honda Pilot/Odyssey throws B2740 from a known driver-door master-switch board solder-crack issue, with aftermarket reman boards available for $30. Estimated repair: $40 (aftermarket switch DIY) to $550 (OEM switch plus door-jamb wiring repair on a truck).