In gasoline engines, the spark plugs are used to burn the fuel. On the other hand, diesel engines, although they do not use spark plugs because the fuel is burned by compression, they do have glow plugs. These components are very important for diesel engines when working in cold weather.
The main function of the heaters is to increase the temperature of the engine, especially during cold weather or if the engine has been idle for a certain time. It should be noted that the diesel engine needs a high level of heat because diesel just explodes under high compression at high temperatures. These heaters also reduce engine emissions by up to 49% because with the engine at a warmer temperature, the fuel burns easily.
The Fault code P0671 OBDII indicates that there is a problem in the glow plug circuit, resulting in the number 1 cylinder plug not heating up.