C (104° F) with a 12 Volt supply.
The glow plug control module (GPCM) is located in the engine bay on the right-hand side. It
acts as a switch for the current to the glow plugs and is controlled via the engine control
module (ECM). Above a given coolant temperature, glow plugs will not be switched on
before, during or after starting. Within a certain coolant temperature range, the glow plugs
will be active before cranking to increase combustion chamber temperature, during cranking
to assist engine starting, and after the engine has started in order to reduce the emissions of
white and possibility black smoke from the tail pipe immediately following a cold start.
The ECM is connected to the GPCM via a reference control line and a diagnostic line. The
former will be pulled down by the ECM causing the GPCM to switch on and to remain
switched on while the reference voltage is low. The ECM will store the error information
generated by the GPCM in the case of glow plug failure.