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U0645 Lost Communication With Active Air Dam Module

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

An active air dam is a motor-driven panel below the front bumper that drops at highway speed to cut drag and retracts for low speed or rough ground. Its small control module talks to the powertrain controller over a serial line; on the 2.7L F-150 Ford runs it on a LIN bus shared with the generator and the grille shutters. U0645 is logged once that module no longer replies. Ram uses it on the 1500 DT: TSB 23-029-22 covers 2019 trucks built up to 21 January 2019 (sales code MXB) with the MIL lit, and a new air dam under an eight-year warranty extension. A 2025 Ram case asks for impact damage, connector corrosion and resistance checks first. Ford's SSM 50737 blames a LIN wire grounded at the left engine mount. Actuator faults are C0601 to C0630.

Likely causes

Air dam unit with built-in module failed (early Ram 1500 DT)

Air dam damaged by curb, snow or debris impact

Water or corrosion in the air dam connector

Shared LIN wire chafed to ground near the engine mount (Ford F-150 2.7L)

Symptoms

Air dam stays in one position
Check engine light on some trucks (Ram)
Charging system warning if the shared LIN line is shorted (Ford)

Repair estimate

DifficultyMediumDIY possible

Parts and labour€40–900

Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

active air dam modulevehicle bus wiring

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov, law.cornell.edu.