An aftermarket telematics system for use with a vehicle having a vehicle bus is disclosed herein. The aftermarket telematics system includes, but is not limited to, an aftermarket telematics unit that is configured to be mounted to the vehicle, to communicate with the vehicle bus, and to detect when the vehicle has been turned off. The aftermarket telematics system also includes a vehicle communication interface device configured to connect to the vehicle bus, to be communicatively coupled with the aftermarket telematics unit, and to facilitate communication between the aftermarket telematics unit and the vehicle bus. The aftermarket telematics unit is further configured to send a sleep command to the vehicle communication interface device when the aftermarket telematics unit detects that the vehicle has been turned off. The vehicle communication interface device is configured to sleep in accordance with the sleep command.