WiiYii OBD2 GPS HUD Car On-board Computer 4.3" HD TFT Digital Speed Projector OBD Head Up Display Coolant Fuel Fault Code Clear T800is a GPS speedometer, can work for all the vehicles,but only simple functions. P12is a OBD on-board computer, can display many functions if compatiable. However, it only works with some cars after 2008. Details pls can't with our sales. T812is OBD+GPS 2 in 1 device. If OBD2 protocol is compatible with your car, it will show many functions, speed, voltage, mileage, fuel consumption, water temperature, read errors, fault Code clear and so on. If OBD2 protocol is not compatible with your car, GPS chipset will work and it could show you the speed and voltage also.P12--- T800---T812--- Product Differance: Model P12 T800 T812 Chipset OBD2 GPS GPS+OBD Display Information Speed, RPM , Fuel Consumption ,Voltage, Water Temperature, Trip Mileage,Trip Time,Total Mileage , Turbo boost ,Oil Temperature Time ,Speed,Voltage, Altitude , Compass , Trip Mileage,Trip Time Speed, RPM,Fuel Consumption,Voltage, Water Temperature, Trip Mileage,Trip Time, Total Mileage,Turbo boost, Oil Temperature Altitude , Compass , Test Brake Test,Speedup Test Brake Test,Speedup Test Brake Test,Speedup Test Alarm RPM Alarm Water Temperature Alarm Low Voltage AlarmFaulty Code Alarm Voltage Alarm RPM Alarm Water Temperature Alarm Low Voltage Alarm Faulty Code Alarm Applied to ONLY cars after 2008 with open obd2 protocol,details car model, pls contact with us works with all cars works with all cars Dual System OBD2+GPS 2 in 1 Car On-board Computer HUD T812: GPS Speedometer T800: On-board Computer OBD2 HUD P12: