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

What it means

The vehicle bus reports loss of communication with smart turbocharger bypass valve B position sensor. Closed-loop control loses its actual feedback.

At a glance

• Usually lights the warning light of the system that lost communication
• Affects emissions; the car can fail an emissions test

How it works

The turbocharger or supercharger bypass valve controls airflow around the boost-producing unit, and its B position sensor reports the valve's actual position over the vehicle network. The control module sets U066B when it can no longer receive messages from that sensor, so it cannot compare the reported position with the commanded one.

Common causes

Most likely first.

1. Bus wiring open or shorted
2. Module without power or ground
3. Module failed

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Scan all modules for communication codes and review freeze-frame data to see whether other devices on the same network dropped out at the same time.
2. Use a scan tool to check whether bypass valve B is listed as present and whether its position data updates when the engine is running or the valve is commanded.
3. Inspect the sensor B connector and nearby harness for looseness, corrosion, heat damage, or chafing around the bypass valve.
4. Check the sensor's power and ground and inspect the network wiring for opens, shorts, or poor connections using the manufacturer's wiring information.
5. If wiring, power, and ground are sound, test network communication at the sensor and determine whether the sensor module itself has failed.

Common fixes

• Reconnect or clean the bypass valve B sensor connector and repair damaged wiring.
• Restore a missing power or ground connection to the sensor.
• Repair an open or short in the vehicle network wiring to sensor B.
• Replace the bypass valve B position sensor if its power, ground, and network connections are good but it remains offline.

Can I keep driving?

If the engine runs normally and there are no boost or drivability symptoms, a short, gentle trip may be possible, but avoid hard acceleration or towing because bypass control feedback is unavailable. Stop if power drops sharply or warning lights indicate a more serious fault.