Glow plugs in the diesel engine are small 12 V heating elements with the tip exposed to a small chamber where the volume of air can readily be heated. When the diesel engine is started up, the glow plug preheating current is controlled, taking into account factors such as coolant temperature. In addition to shortening preheating time, the surface temperature of the glow plug is maintained at a fixed temperature after the engine has been started. This has the effect of stabilizing engine speed and reducing the amount of smoke. The preheating warning light (GLOW LAMP), which is located on the cluster, notifies the driver that the ECM is preheating it to improve the driving performance.