Corroded, loose, or backed-out pins in the EGR sensor E electrical connector.; Chafed or broken wiring in the harness between the EGR sensor and the module that reports it on the CAN bus.; Failed EGR sensor E internal electronics that prevent it from responding to network requests.; A faulty or intermittently failing control module that acts as the gateway or reporter for that sensor on the bus.; Low battery voltage or poor grounds causing modules to drop off the network intermittently.; Aftermarket accessories or poor previous repairs introducing CAN bus interference or incorrect termination.; Water intrusion into a connector or module housing that corrodes the communication circuit.

DTC codes / U06xx · Network communication / U066A

U066ALost Communication With EGR Sensor E

Q: What does code U066A mean?

Lost Communication With EGR Sensor E. U066A is a generic network communication code indicating that a control module on the vehicle's controller area network (CAN) bus has lost contact with the exhaust gas recirculation (EGR) sensor designated as E. The computer detected that expected periodic messages from that sensor or its associated module stopped arriving within the required time window, so it flagged the communication loss rather than a direct sensor performance fault.

U066A is a generic network communication code indicating that a control module on the vehicle's controller area network (CAN) bus has lost contact with the exhaust gas recirculation (EGR) sensor designated as E. The computer detected that expected periodic messages from that sensor or its associated module stopped arriving within the required time window, so it flagged the communication loss rather than a direct sensor performance fault.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaNetwork communication

Symptoms you may notice

Illumination of the check engine light or service vehicle soon message with no other obvious dashboard warnings.
Often no symptoms besides the warning light, especially if the EGR system is not actively being commanded during normal driving.
Intermittent rough idle or slight hesitation when the engine is cold and the EGR system is being tested.
A stored pending or history code that reappears after clearing, particularly in damp or cold weather.
Possible reduced fuel economy if the powertrain control module substitutes a default EGR strategy.
Other communication-related codes stored in multiple modules if the fault is on a shared bus segment.

Common causes, most likely first

Corroded, loose, or backed-out pins in the EGR sensor E electrical connector.
Chafed or broken wiring in the harness between the EGR sensor and the module that reports it on the CAN bus.
Failed EGR sensor E internal electronics that prevent it from responding to network requests.
A faulty or intermittently failing control module that acts as the gateway or reporter for that sensor on the bus.
Low battery voltage or poor grounds causing modules to drop off the network intermittently.
Aftermarket accessories or poor previous repairs introducing CAN bus interference or incorrect termination.
Water intrusion into a connector or module housing that corrodes the communication circuit.

How to diagnose and fix it

Record all stored codes and freeze-frame data from every module before clearing anything, then verify U066A returns after a test drive.
Inspect the EGR sensor E connector and the module connector for corrosion, loose pins, and pushed-out terminals; clean and reseat as needed.
Perform a voltage drop and continuity test on the CAN bus wiring and the sensor's power and ground circuits using a wiring diagram for the specific vehicle.
Check battery state of health and charging voltage, and verify all ground straps and module grounds are clean and tight.
Substitute a known-good EGR sensor E only after wiring and power checks pass, then clear codes and confirm communication restores.
If the sensor is not the issue, scope the CAN bus for correct differential voltage and termination, and check for modules that are pulling the bus down.
As a last step, follow the manufacturer's diagnostic flow for the reporting module, including software updates or module replacement if the bus itself tests good.

What the EGR sensor E code hides

U066A is a communication code, not a performance code, so replacing the EGR sensor without checking the connector and wiring first is the most common misdiagnosis.
A weak battery or a failing ground can drop a module off the CAN bus long enough to set U066A without ever leaving a low-voltage code in memory.
The sensor may be reported by a different module than the one that directly wires to it, so the fault can live in a gateway or body module rather than at the sensor.
Intermittent U066A that appears only in wet weather usually points to water intrusion in a connector or harness splice, not a failed sensor.
Aftermarket remote starters, alarms, or poorly installed accessories tapped into the CAN bus can corrupt messages and trigger communication codes like this one.

Can I keep driving with U066A?

The vehicle is generally safe to drive because the fault is a communication loss, not a mechanical failure, but avoid long trips or heavy load until the cause is found since the EGR system may be disabled and emissions can increase. If the warning light flashes or the engine runs poorly, stop driving and have it diagnosed promptly.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.