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U066B Lost Communication With Turbocharger/Supercharger Bypass Valve B Position Sensor

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

When the throttle snaps shut, a compressor bypass valve lets boosted air recirculate to the inlet side instead of surging against the closed plate. Engines with two chargers or two compressor stages can carry a second such valve, and if its electric actuator reports the opening angle as a digital message, U066B means the engine controller no longer gets valid position frames from valve B. No manufacturer documents this code publicly. Ford's 2024 gasoline summary checks bypass valve B only for circuit faults (P00C1/P00C2 after 5 s) and lists no position feedback for it. Analog position faults on valve B would be P2C2A to P2C2C; valve A has U0657. CARB demands a separate code for lost communication of digital inputs. Boost is usually limited.

Likely causes

Signal, supply or ground wire to the bypass valve B actuator damaged

Connector at the valve loose, corroded or heat-damaged near the turbo

Position sensor electronics in the valve actuator failed

Engine controller input or software fault

Symptoms

Check engine light
Boost limited, reduced power
Compressor surge noise when lifting off the throttle

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€60–700

Time0.5–2.5 h

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

Parts involved

turbo bypass valve b position sensorvehicle bus wiring

References: law.cornell.edu, fordservicecontent.com, en.wikipedia.org.