U0669 means the powertrain control module has lost serial communication with the EGR system’s “Sensor D” circuit. It is a network/communication fault rather than a direct sensor-performance fault, so the issue usually lies in the data line, power/ground, connector, or the sensor module itself. The engine may run normally or show only emission-related symptoms while the code is active.
The sensor’s internal communication circuit can fail, preventing it from responding on the bus even though power and wiring are intact.
Open, shorted, pinched, corroded, or loose terminals in the harness between the sensor and the PCM can interrupt communication.
A missing or weak ignition/ battery feed, blown fuse, or poor ground can keep the sensor from powering up and communicating.
A fault in the shared LIN, CAN, or dedicated sensor bus—such as a short, open, or excessive resistance—can isolate the sensor from the PCM.
A damaged PCM communication driver is possible but uncommon; it should only be considered after wiring, power, ground, and the sensor have been ruled out.
Usually yes for normal driving, but the fault can affect emissions control and may cause a failed emissions test; have it diagnosed promptly.
No—PCM failure is rare for this code. Most U0669 faults are caused by the EGR sensor, its connector, wiring, power/ground, or the data bus.
It is a manufacturer-specific identifier for a particular EGR-related sensor or sub-module circuit, which may be a position, pressure, temperature, or integrated valve sensor on a serial bus.
Not necessarily. The code points to a communication failure, not a mechanical EGR valve failure. The valve may be fine while the sensor, wiring, or bus is at fault.