U0644: Lost Communication With Wastegate Position Sensor A

What it means

A control module has stopped receiving expected network messages from wastegate position sensor A. The effect on boost control and engine performance depends on the vehicle's system design.

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

Wastegate position sensor A reports the position of the turbocharger wastegate so the control system can manage boost. U0644 sets when a control module stops receiving the expected network messages from this sensor, which can leave wastegate position unknown and trigger reduced-power operation.

Common causes

Most likely first.

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

Symptoms

• Warning light or message related to the affected system
• Engine performance may be affected

How to diagnose it

1. Scan all modules, save freeze-frame data, and note any boost-control or communication codes that could identify when wastegate position messages stopped.
2. Check live data for wastegate position sensor A and confirm whether the reading is missing or invalid.
3. Inspect the sensor A module connector and nearby network wiring for damage, corrosion, or a loose connection.
4. Check the module’s power and ground circuits against the manufacturer’s specification.
5. Test the network bus wiring serving wastegate position sensor A for opens or shorts using the vehicle wiring information.
6. If the circuits are intact, verify network communication and module operation before replacing the sensor module.

Common fixes

• Secure or clean the wastegate position sensor A connector.
• Repair damaged network wiring to sensor A.
• Restore the sensor module’s power or ground supply.
• Replace the failed wastegate position sensor A module after its wiring and supplies pass testing.

Can I keep driving?

Because boost control may be limited or unpredictable, avoid high speeds, hard acceleration, and towing; arrange prompt diagnosis. Stop driving if the engine loses substantial power, runs abnormally, or a temperature warning appears.