P0108

P0108 means MAP signal voltage is above the ceiling — over 4.9V on a 1-bar sensor with the engine running at idle, or over 4.9V on a 3-bar sensor at non-boost conditions. The sensor is reporting maximum pressure when the actual manifold pressure should be vacuum at idle. Cheapest-first ladder: check the vacuum reference first — a disconnected or clogged vacuum hose between the manifold and the MAP sensor will set P0108 instantly because the sensor reads atmospheric (which on a 1-bar sensor IS the ceiling) instead of idle vacuum; pull the MAP and inspect the port for carbon blockage on direct-injection engines (very common on VW/Audi 2.0T, BMW N54, Ford EcoBoost — the manifold port chokes with carbon and the sensor reads ambient cabin air pressure); back-probe the signal wire engine running at warm idle, must be 1.0-1.5V on a 1-bar at idle vacuum of 30-40 kPa — if signal voltage is 4.7V at idle the sensor is seeing atmospheric, which is mechanical not electrical; verify the 5V reference is not shorted to the signal wire by ohming the sensor with the connector unplugged; verify ground integrity. A P0108 on a turbo engine at idle is mechanical 95% of the time — clogged port or disconnected hose — and replacing the sensor will not fix it.

Vehicle-specific patterns: 2008-2014 VW/Audi 2.0T TSI (CCTA, CBFA, CAEB) sets P0108 from carbon plugging the MAP sensor port in the intake manifold, requiring walnut-blast intake cleaning before the sensor can read correctly; 2007-2013 GM 5.3L Silverado/Tahoe sees P0108 when the MAP sensor port under the intake manifold valley cover gets blocked by oil residue from AFM-related blow-by; 2007-2018 Cummins 5.9L/6.7L Ram sees P0108 from soot completely plugging the intake horn MAP port to where atmospheric air cannot reach the silicon element; 2010-2016 BMW N20/N55 sets P0108 from carbon buildup on intake valves restricting actual MAP reading combined with sensor port partial blockage. Estimated repair: $40 to $600.