P0242

P0242 is the bank-2 / sensor-B boost-pressure sensor 'circuit low' fault - the signal voltage has dropped below the lower electrical threshold the ECU monitors, typically below 0.25V (well under what a healthy sensor reads even at atmospheric pressure). This is a hard circuit code, not a performance code, which means the fault is electrical: a wiring short to ground, a dead sensor with internal shorted output, or a missing 5V reference. Diagnostic order on a shop floor: (1) Disconnect the sensor and read voltage at the signal pin of the connector with KOEO - a healthy 5V reference and a floating signal mean the sensor is the failed component; if the signal pin reads zero with the sensor disconnected, the harness is shorted to ground somewhere between the sensor and the ECU. (2) Check the 5V reference at the connector - many boost sensors share a 5V bus with other sensors (MAP, TPS), so a shorted boost sensor can pull the entire 5V bus down and throw multiple codes at once; if you see P0242 plus P0123 or P0108 simultaneously, the boost sensor shorting the bus is the most likely root cause. (3) Wiggle-test the harness around any clip points where the wiring routes near hot exhaust or sharp brackets - chafed insulation that shorts to a ground plane is a classic intermittent P0242. The 15-minute DMM check almost always nails the fault to either harness or sensor before any parts are bought.

Vehicle-specific patterns: 2008-2013 BMW N63 twin-turbo V8 (550i, 750i, X5/X6 5.0i) commonly throws P0242 from a failed boost-pressure sensor on the bank-2 charge pipe - heat-soak under the V8 cooks the sensor electronics. 2011-2016 Ford F-150 3.5L EcoBoost throws P0242 from chafed sensor wiring at the intercooler-pipe bracket on the passenger side; Ford TSB coverage exists for harness retainers on early-build trucks. 2007-2010 BMW 135i / 335i / 535i with the N54 throws P0242 from a connector pin that backs out under vibration - re-seat and dielectric-grease the connector before quoting a sensor. 2013-2018 Chevy Cruze 1.4L / 1.8L turbo and Sonic 1.4L turbo throw P0242 from a failing post-intercooler MAP sensor (referenced as sensor B in service data) that GM has a known supplier-quality issue with. Estimated repair: $75 to $400