P0109

P0109 is the intermittent MAP code — the ECM saw an out-of-range MAP signal that recovered before latching a P0107 or P0108, and it has happened enough times to set a code. Like P0104 for MAF, these are diagnosis-heavy because the fault is rarely present in the bay. Cheapest-first ladder: wiggle-test the MAP connector and the 6-12 inches of harness behind it with engine running and a scan tool recording MAP kPa — any spike from 35 kPa idle to 100 kPa, or drop to 0 kPa, confirms the fault zone; inspect the connector for pushed-back terminals and oil contamination (oil in the connector body is a leading cause of intermittent MAP signal on Chrysler Hemi and GM trucks); check the vacuum reference hose for a partial restriction that intermittently clears — a wad of carbon that sits in the port and gets blown clear at high RPM will set P0109 repeatedly; clean the MAP port with carb cleaner if the engine is direct-injection because carbon partial blockage is the most common P0109 cause on VW/Audi, BMW, and Ford EcoBoost; leave a scan tool recording freeze-frames during the customer's normal drive cycle if bay-side testing comes up clean. Replacing the MAP for P0109 without a wiggle test and a vacuum-port inspection is the most common misdiagnosis in this code — the sensor is usually fine.

Vehicle-specific patterns: 2008-2014 VW/Audi 2.0T TSI sets P0109 from partial carbon blockage of the MAP port that clears and re-blocks with engine vibration; 2005-2010 Chrysler 5.7L Hemi sees P0109 from oil contamination wicking into the MAP connector intermittently shorting the signal pin; 2007-2014 GM 5.3L sees P0109 from the under-intake MAP picking up intermittent moisture from a slow intake gasket coolant weep; 2007-2018 Cummins 5.9L/6.7L Ram sees P0109 from soot intermittently bridging the MAP signal circuit before fully clogging the port. Estimated repair: $30 to $450.