P2078

P2078 is the bank-2 intake-manifold tuning valve position sensor 'circuit low' fault - the position-sensor signal voltage has fallen below the lower electrical threshold, typically below 0.2V on a 5V-referenced potentiometer. Unlike P2077 (range/performance, where the sensor reports an implausible value), P2078 is a hard electrical fault: the wire is shorted to ground, the sensor's wiper has lost contact with its track, or the harness is broken. Cheapest-first ladder: (1) Disconnect the sensor and read signal-wire voltage at the connector KOEO - a stuck-low signal with the sensor unplugged means the harness is shorted to ground between the sensor and the ECU; a normal 2.5V floating reading with the sensor unplugged means the sensor itself is the failure. (2) Visually inspect the sensor housing for cracking or moisture intrusion - IMRC position sensors mounted on top of intake manifolds get heat-cycled and crack open over time. (3) Confirm 5V reference and ground at the sensor connector - a shared 5V bus with another shorted sensor can drag this signal down too. Expensive-misdiagnosis trap: replacing the IMRC actuator-with-integrated-sensor assembly when the standalone sensor or a $50 harness repair would have fixed it.

Vehicle-specific patterns: 2008-2013 Audi / VW 3.6L VR6 FSI in Touareg / Q7 / Passat throws P2078 from a failed intake-flap position sensor on the bank-2 side - VW issued a part-number update on the motor/sensor assembly. 2006-2010 Mercedes-Benz M272 V6 (C350, E350, R350) throws P2078 from a known intake-manifold runner-flap sensor fault (sometimes combined with the larger balance-shaft gear wear issue). 2009-2014 Hyundai Genesis sedan 3.8L (Lambda II V6) throws P2078 from a runner-control sensor that loses signal as the connector ages. 2007-2013 Cadillac STS / CTS with the 3.6L LLT throws P2078 from harness chafing near the throttle body. Estimated repair: $90 to $650