The glow control unit of the glow system employs the method of energizing the glow plug of each cylinder respectively.
The glow control unit carries out the duty control to the energisation of the glow plug, in accordance with the signal from the engine-ECU. This achieves the optimum voltage of the glow plug in accordance with the engine conditions at the after glow to stabilize the combustion. Also the combustion noise or hydrocarbon (HC) emissions are reduced.

System Configuration Diagram

The engine-ECU determines the glow start, the glow time and the energisation duty cycle of the glow plug. The engine-ECU outputs the PWM signal of the glow operation request to the glow control unit when the following conditions are satisfied.
Before starting (Pre-glow control)
Under the conditions of the engine not starting, the maximum energisation time of the glow plug (duty of 100%) is 20 seconds.
While running a cold engine (After-glow control)
note The glow duty is determined in accordance with the engine coolant temperature and the intake air temperature (at the air flow sensor).
The maximum energisation time of the glow plug is 300 seconds.

Glow Indicator Lamp Control

When the engine coolant temperature is below a predetermined level, the engine-ECU sends a signal to the combination meter via CAN (Controller Area Network) to request the illumination of the glow indicator lamp. This causes the glow indicator lamp to illuminate, in order to inform the driver of the timing for starting the engine.


The glow control unit is installed in the relay box of the engine compartment. The engine-ECU supplies the power to the control part of the glow control unit when the ignition switch is turned ON. The energisation to the glow plug from the battery is controlled by installing the power-MOSFET (Metal Oxide Semiconductor Field Effect Transistor) to the glow control unit for each cylinder. When receiving the signal from the engine-ECU through the control signal wire, the glow control unit controls the Power-MOSFET, based on the signal duty, to control the voltage for each glow plug. If detecting the open or short circuit of the glow plug, or communication failures to the engine-ECU, the glow control unit sends the malfunction signal to the engine-ECU through the diagnosis signal wire.


The glow plug is installed to each cylinder of the cylinder head. The glow plug performs preheating of the combustion chamber with the ceramic heating element on the acral part. The heating temperature of the glow plug is changed by adjusting the voltage applied to the glow plug through the duty control of the glow control unit.

The self control resistance is built in the ceramic heating element of the glow plug. When the current is going through the glow plug, the heating element heats up and the self control resistance increases, too. This gradually decreases the current going through the heating element to restrict the amount of heating the glow plug.