What it means
A control module received invalid data from digital disc player/changer module D. The code identifies a data validity fault; the specific affected function depends on the vehicle.
How it works
Digital disc player/changer module D manages disc playback and sends track, slot, and fault information over the vehicle network. U0491 sets when a receiving module rejects data from module D because it fails validity checks.
Common causes
Most likely first.
- Fault in the transmitting module
- Network wiring or connector fault
- Module power or ground fault
- Software or configuration mismatch
Symptoms
- Disc player or related audio functions may not work correctly
- Infotainment warning or related communication codes may appear
How to diagnose it
- Scan all modules and save freeze-frame details, noting which module stored U0491 and any disc player, infotainment, or network codes.
- Check module D’s playback, track display, and slot controls to see whether its functions fail separately from other disc units.
- Inspect module D’s connector and accessible network wiring for looseness, corrosion, moisture, or damage.
- Check module D’s power and ground using the manufacturer’s procedure before replacing the unit.
- Use a vehicle-capable scan tool to review module D’s reported status and verify software or configuration compatibility, especially after a replacement.
- If wiring and supply are sound, follow the manufacturer’s network tests to determine whether module D or the gateway is responsible for the invalid data.
Common fixes
- Reconnect or repair a loose or damaged module D connector or network wire.
- Repair module D’s power or ground connection.
- Correct software or configuration mismatches after replacing module D or related equipment.
- Replace module D or repair the gateway after tests identify the failing source.
Can I keep driving?
If the fault only affects module D’s disc or infotainment functions, driving is generally unaffected. Promptly investigate any warnings or loss of function in other vehicle systems.
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.