Some Eonon Volkswagen-specific head unit users may notice a phenomenon: when the car engine is not started and the key is turned to the ACC or ON position, the audio system may produce intermittent sound or no output. Once the engine is started, the audio returns to normal.
This issue is not caused by a fault in the head unit or speakers. Instead, it is related to the factory amplifier control mechanism built into the vehicle. In this blog, we’ll explain why this happens and provide some guidance on proper usage.
How the Factory Amplifier Works
In many Volkswagen vehicles, the factory audio system includes a dedicated amplifier to power the speakers and improve sound quality.
When an Eonon Volkswagen-specific head unit is installed, the system typically communicates with the vehicle’s electronics through a CANBUS decoder box, which handles functions such as:
- Steering wheel controls
- Vehicle information display
- Factory amplifier activation
The CANBUS decoder box determines whether to send power signals to the factory amplifier based on the car’s current status.
Why There May Be No Sound in ACC Mode
When the vehicle is only in ACC or ON mode (power to electronics but engine off), the CANBUS decoder box usually does not activate the factory amplifier.
As a result, you may experience:
- The factory amplifier is not powered
- Speakers receive intermittent or no audio signal
- Sound output may be unstable or completely muted
Once the engine is started, the vehicle electronics fully activate, and the CANBUS decoder box sends a signal to power the amplifier, restoring normal audio performance.
Why This Behavior Exists
This is a normal design in factory audio systems and primarily serves to protect the car battery.
Continuously powering the amplifier when the engine is off could lead to:
- Rapid battery drain
- Risk of the vehicle not starting
- Increased strain on the battery
Therefore, some vehicles intentionally limit amplifier operation in ACC mode to avoid unnecessary power consumption.
The Role of the CAN BUS Decoder Box
The CAN BUS decoder box is a key component in modern car audio systems. It not only controls the amplifier but also translates factory signals for the head unit.
Other important functions of the CAN BUS decoder box include:
- Steering wheel control support – enables volume adjustments, call handling, and media control from the wheel
- Vehicle information display – sends signals like temperature, fuel level, and system alerts to the head unit
It essentially acts as a bridge between the head unit and the original vehicle electronics.
Recommended Usage
To ensure stable operation of the factory amplifier and speakers, we recommend:
- Start the engine before using the audio system
- Avoid long-term audio playback while in ACC mode
This ensures stable audio performance while also protecting the car battery.
Conclusion
If your saiho Volkswagen-specific head unit produces no sound or intermittent sound in ACC mode, this is typically normal behavior due to CAN BUS-controlled factory amplifier operation and not a malfunction.
Once the engine is running, the amplifier will activate, and audio output will return to normal.
If issues persist, you can contact the saiho support team for further assistance at rita@saiho.com