Voice commands
Say 'Hey Google', press and hold the voice command button on your steering wheel or select the microphone 
Here are some things that you can try if Android Auto is having trouble understanding voice commands:
- If you're using the voice command button on your steering wheel, make sure that you press and hold until you hear the beep. If you don't press it long enough you might exit Android Auto and have to restart it.
- Start speaking after you hear the Android Auto beep. The beep is confirmation that Android Auto is listening.
- Try to minimise the noise around you when you speak.
- If you're using an aftermarket receiver, make sure that your microphone is working properly. You can check with your installer if you're not sure.
Volume
In some vehicles, the volumes for navigation, media and voice may be controlled separately. Please consult your vehicle owner's manual to find out more.