What it means
A control module has received data from the cruise control front distance range sensor that it considers invalid or implausible. Adaptive cruise or related functions may be affected; the specific effects depend on the vehicle.
How it works
The cruise control front distance range sensor measures the road ahead so adaptive cruise can adjust following distance. U0406 is set when a receiving module rejects the sensor's distance or status data as implausible or incompatible with the system configuration.
Common causes
Most likely first.
- Implausible or incorrect distance sensor data
- Sensor or module fault
- Software or configuration incompatibility
Symptoms
- Adaptive cruise or related functions may be unavailable
- Related warning indicators may illuminate
- A diagnostic scan may show related communication codes
How to diagnose it
- Scan all modules and save freeze-frame data to identify related adaptive cruise or sensor codes and the conditions when U0406 appeared.
- Check the front distance sensor face and its field of view for dirt, ice, damage, or anything obstructing it.
- Inspect the sensor mount, connector, and wiring for impact damage, misalignment, corrosion, or loose connections.
- Review live sensor status and distance data to see whether readings are absent, erratic, or inconsistent with the visible road conditions.
- If the sensor and wiring appear sound, verify the sensor and related module configuration and follow the vehicle's specified alignment or calibration procedure.
Common fixes
- Clean the sensor face and remove any obstruction from its field of view.
- Repair damaged sensor wiring or connectors.
- Correct sensor mounting or alignment using the vehicle's specified procedure.
- Update or configure the related module if a software mismatch is confirmed.
- Replace a faulty front distance range sensor after testing confirms the fault.
Can I keep driving?
Adaptive cruise or related distance functions may be unavailable or unreliable. Drive manually, leave extra following distance, and do not rely on automatic braking or distance control until the system is confirmed to work.
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.