U066B code meaning
Lost Communication With Turbocharger/Supercharger Bypass Valve B Position Sensor
Network system Generic code U06xx codes Check engine light
What U066B means
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.
U066B at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 2.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U066B
- Check engine light
- Boost limited, reduced power
- Compressor surge noise when lifting off the throttle
Common causes of U066B
- Most likelySignal, supply or ground wire to the bypass valve B actuator damaged
- PossibleConnector at the valve loose, corroded or heat-damaged near the turbo
- PossiblePosition sensor electronics in the valve actuator failed
- Less likelyEngine controller input or software fault
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Turbo bypass valve b position sensorVehicle bus wiring
What each part of U066B means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 6B | The exact fault in that area. |
What to do next
- Note U066B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U066B
What does U066B mean?
U066B means "Lost Communication With Turbocharger/Supercharger Bypass Valve B Position Sensor". When the throttle snaps shut, a compressor bypass valve lets boosted air recirculate to the inlet side instead of surging against the closed plate. It is a generic code, so it means the same on every make.
Is it safe to drive with U066B?
Drive gently and only to a workshop. With U066B the car can go into limp mode (reduced power) to protect itself.
Will U066B fail an emissions test?
Yes, it can. U066B is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U066B to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. This is a job for a workshop.
Will U066B clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.