What it means
The vehicle bus reports loss of communication with smart EGR sensor D (position or flow). EGR 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
EGR sensor D reports position or flow information used by the engine controller to regulate exhaust gas recirculation. U0669 sets when network messages from sensor D stop arriving, so the controller loses normal feedback for EGR operation and may store emissions-related faults.
Common causes
Most likely first.
- Bus wiring open or shorted
- Module without power or ground
- 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
- Scan the engine and network modules, save freeze-frame data, and check for related EGR position, flow, or communication codes.
- Review live data for EGR sensor D and compare its reported status with commanded EGR operation, where the scan tool provides both.
- Inspect sensor D's connector and harness for looseness, corrosion, heat damage, or chafing near the EGR assembly.
- Check sensor D's specified power and ground under load, using the wiring diagram to identify shared feeds.
- Test the network circuit serving EGR sensor D for opens, shorts, or abnormal resistance according to the manufacturer procedure.
- If its supply and bus wiring pass, follow the manufacturer's sensor communication and EGR diagnostic steps before replacing sensor D.
Common fixes
- Reconnect and secure the EGR sensor D connector.
- Repair heat-damaged, chafed, or corroded wiring at sensor D.
- Restore a faulty power or ground feed to the sensor.
- Repair an open or short in the network wiring serving EGR sensor D.
- Replace EGR sensor D after its power, ground, and communication circuit pass testing.
Can I keep driving?
Driving may be possible if the engine runs normally, but EGR feedback loss can increase emissions and may cause poor running or reduced performance. Avoid extended driving if the engine misfires, smokes heavily, or loses power, and arrange prompt diagnosis.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.