Damaged or disconnected wiring harness at the bypass valve position sensor connector.; Corroded or loose electrical terminals in the sensor connector or at the control module.; Failed bypass valve position sensor itself, internal open or short circuit.; Blown fuse or poor ground connection shared by the sensor circuit.; Communication bus fault such as a shorted or open data line between the sensor and the module.; Failed control module that is no longer transmitting or receiving on the network.; Aftermarket electronic modifications or poor previous repairs disturbing the harness.

DTC codes / U06xx · Network communication / U066B

U066BLost Communication With Turbocharger/Supercharger Bypass Valve B Position Sensor

U066B is a generic network communication code indicating that a control module has lost contact with the position sensor for the 'B' turbocharger or supercharger bypass valve. The computer detected that the expected data messages from that sensor stopped arriving over the vehicle's communication bus, which prevents the engine computer from knowing the valve's actual position.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaNetwork communication

Symptoms you may notice

Illumination of the check engine light or service vehicle soon message, often with no other symptoms.
Reduced engine power or limp mode because the bypass valve position is unknown.
Poor throttle response or hesitation during acceleration.
Rough idle or stalling when the bypass valve fails to modulate boost as expected.
A noticeable whistle or whoosh from the turbocharger area if the valve sticks open or closed.
Fuel economy may drop as the engine management system defaults to a safe boost strategy.

Common causes, most likely first

Damaged or disconnected wiring harness at the bypass valve position sensor connector.
Corroded or loose electrical terminals in the sensor connector or at the control module.
Failed bypass valve position sensor itself, internal open or short circuit.
Blown fuse or poor ground connection shared by the sensor circuit.
Communication bus fault such as a shorted or open data line between the sensor and the module.
Failed control module that is no longer transmitting or receiving on the network.
Aftermarket electronic modifications or poor previous repairs disturbing the harness.

How to diagnose and fix it

Inspect the bypass valve position sensor connector and wiring for obvious damage, corrosion, or loose pins.
Check the sensor circuit fuse and verify good ground at the sensor connector with a multimeter.
Measure sensor reference voltage and signal voltage at the connector to confirm power and ground are present.
Perform a wiggle test on the harness while watching live sensor position data to reveal intermittent faults.
Check communication bus continuity and resistance between the sensor and the control module.
If wiring and power are good, substitute a known-good sensor and clear the code to see if it returns.
As a last step, verify the control module is functioning correctly and update or replace it only after all other checks pass.

Why the bypass valve sensor loses communication

A common oversight is assuming the sensor itself has failed when the real problem is a chafed wire behind the engine block that only loses contact on bumps.
This code can set intermittently from water intrusion into the connector after steam cleaning or heavy rain, leaving no permanent fault.
A weak battery or charging system can cause multiple U-codes including U066B because low voltage disrupts network messages.
Some vehicles share the bypass valve position sensor signal with other sensors on the same bus, so a fault elsewhere can mimic this code.
Clearing the code without checking freeze-frame data often leads to a comeback because the original conditions that triggered the fault are missed.

Can I keep driving with U066B?

You can usually drive the vehicle to a repair shop, but avoid heavy acceleration or towing because the engine may enter limp mode and boost control is compromised. If the engine runs poorly or stalls, stop driving and have it towed.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.