Glow Plug System: Description and Operation

Glow Plug System Description

Glow Plug Operation

In the diesel engine, air alone is compressed in the cylinder. Then, after the air has been compressed, a charge of fuel is sprayed into the cylinder and ignition occurs, due to the heat of compression. Eight glow plugs are used as an aid to starting.

Control of the instant start system glow plugs is accomplished by a glow plug control module and 4.7 volt glow plugs, requiring 2 seconds to heat up to 1,000°C (1,832°F). The temperature and the power consumption is controlled between the engine control module (ECM) and the glow plug control module within a wide range to suit the engine's pre-heating requirements. Each glow plug is energized individually. This capability yields more optimum heat times for the glow plugs, thus pre-glow times can be kept to a minimum for short wait to crank times and maximum glow plug durability. A DTC will set if there is a glow plug system fault.

A normal functioning system operates as follows:

* Turn the ignition ON with the engine OFF, and at room temperature.
* The glow plugs turn ON and heat up in 2 seconds and then are pulse-width modulated (PWM) for another 2 seconds.
* The glow plug wait lamp is ON for 1 second during cold start.
* The glow plug wait lamp may not illuminate during a warm engine start.
* If the engine is cranked during or after the above sequence, the glow plugs may cycle ON and OFF after the ignition switch is returned from the start position, whether the engine starts or not. The engine does not have to be running to terminate the glow plug cycling.

The glow plug control module provides glow plug operation after starting a cold engine. This post-start operation is initiated when the ignition switch is returned to Run, from the Start position. This function helps clean up excessive white smoke and/or poor idle quality after starting.

The glow plug initial ON time will vary based on the system voltage and temperature. Lower temperatures cause longer ON times.

Intake Air Heater

The glow plug control module controls and monitors the intake air heater. The ECM sends commands to the glow plug control module to enable or disable the intake air heater when certain conditions met. The glow plug control module monitors the voltage and feedback circuits of the intake air heater to verify proper operation.

Diesel Exhaust Fluid (DEF) Heater Control

The glow plug control module supplies and monitors voltage to the 3 Diesel Exhaust Fluid heaters. The engine control module (ECM) requests any or all of the heaters to be on depending on ambient temperature. The glow plug control module will disable diesel exhaust fluid heater requests from the ECM during glow plug operation.

SmartNOx Boost

The glow plug control module provides a constant voltage to the SmartNox sensors to ensure proper sensor operation. The glow plug control module has internal voltage boosting circuits that will draw more current from the battery when system voltage is low and supply a higher voltage to the SmartNOx sensors in order to maintain proper operation.