My sat nav doesn't work correctly due to an electrical system malfunction.
The GPS doesn't function correctly because of a defect in electrical system.
カーナビはsat nav (satellite navigation)またはGPS(global positioning system)です。
動くwork 機能する function
~のせいで due to ~またはbecause of~。
電気系統の故障 electrical system malfunctionまたはdefect in electrical systemです。