You can create a custom parameter that sets a minimum volume of 1 and up to a maximum of 6.

You can apply the parameter listed below:

<Parameter Description='GoTalk min Volume level=6 (0 to 6)' Offset='175' Bytes='6' IsEnabled='true'/>

You can adjust the volume by varying between 1 and 6 in the Bytes='6' field. 

In this case it is set to 6.

Steps to Configure

• In MyGeotab>Vehicle select the vehicle. 
• Click More Details in the top menu.
• Select the Custom Parameters menu
• Add the parameter listed above and select Add New Parameter