P0240

P0240 indicates the turbocharger boost sensor B circuit is reporting values outside the expected range or failing to track manifold pressure changes correlative with engine load. Start with the cheapest checks: inspect the boost pressure sensor connector for oil contamination from a leaking turbo seal (a $0 visual that catches roughly a third of these), then back-probe the 5V reference and ground at the sensor while watching for a clean signal voltage that should idle around 1.0-1.5V at atmospheric pressure and climb to 2.5-4.5V under boost; flat-lined signals stuck at 0.5V or 4.9V indicate sensor or wiring failure. Compare scan-tool MAP/boost PID against a known-good gauge on a T-fitting before condemning anything, because the expensive misdiagnosis here is replacing the turbocharger ($1,800-$3,500) when a $45 sensor or a cracked charge pipe was the actual fault.

Vehicle-specific patterns: 2011-2016 Ford F-150 3.5L EcoBoost commonly suffers MAP sensor contamination from PCV oil mist, addressed in TSB 14-0194; 2009-2014 VW/Audi 2.0T TSI engines (EA888) crack the charge-pipe-to-throttle-body PCV fitting causing intermittent P0240 alongside lean codes; 2007-2013 BMW N54/N55 throw P0240 when the charge pipe splits at the wastegate-side coupling; 2013-2018 Chevrolet Cruze 1.4L turbo develops cracked intake manifold integrated with the PCV diaphragm. Estimated repair: $80 to $650.