U0674: Lost Communication With Wastegate Position Sensor B

What it means

The vehicle bus reports loss of communication with smart wastegate position sensor B. Closed-loop wastegate control loses its actual feedback; boost falls back to an open-loop fail-safe.

At a glance

• Usually lights the warning light of the system that lost communication
• Affects emissions; the car can fail an emissions test
• The engine or gearbox may go into limp mode

How it works

The turbocharger wastegate regulates exhaust flow through the turbine, and wastegate position sensor B reports the actuator's actual position over the vehicle network. The control module sets U0674 when it loses messages from sensor B, so closed-loop wastegate control loses position feedback and boost may be limited by a fail-safe strategy.

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 sensor B dropped offline with other network devices.
2. Check scan-tool data for wastegate position sensor B's online status and reported position, and compare commanded versus actual position if available.
3. Inspect sensor B's connector and harness at the wastegate for looseness, corrosion, heat damage, or chafing.
4. Using the manufacturer's wiring information, verify sensor power and ground and test the network wires for opens, shorts, or poor connections.
5. If power, ground, and network wiring are sound, test communication at sensor B and determine whether the position sensor module has failed.

Common fixes

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

Can I keep driving?

Drive gently only if the engine has stable power and no unusual boost behavior; avoid hard acceleration, high speeds, and towing because wastegate feedback is unavailable and boost may be restricted. Stop if power becomes unpredictable or another warning signals a serious fault.