To add a little more info
From the FSM:
Jeep CRD 2.8 Glow Plug Operation & Logic Ignition Switch On (Engine Off)
When the ignition is turned on, the ECM activates the glow plug relay for a time period that is determined by engine coolant temperature, atmospheric temperature and battery voltage.
The ECM monitors various engine sensors. When the ignition key is turned to the ON position, the ECM sends a signal to the glow plug module to turn on, and cycle, the glow plugs for a pre-determined amount of time, plus illuminate the glow plug light in the instrument panel. Once activated, the element inside of the ceramic core of the glow plug begins to glow. Each glow plug draws approximately 5 amps, for a total system amperage of 20 amps at 72°F ambient temperature. If there is a fault with the glow plug system, the ECM will store a fault code.
CAUTION: The glow plug system is a 7 volt system.
DO NOT ATTEMPT to test the glow plug system with a 12V power source or damage will occur.
OPERATION: When the ignition (key) switch is placed in the ON position, a signal is sent from the sensors to the ECM relaying current engine coolant temperature and ambient air temperature (Fig. 21).
After receiving this signal, the ECM will determine if, when and for how long of a period the glow plugs should be activated. This is done before, during and after the engine is started. Whenever the glow plug module is activated, it will control the 7 volt high amperage circuit for the operation of the four glow plugs.
The Glow Plug lamp is tied to this circuit. Lamp operation is also controlled by the ECM. With a cold engine, the glow plug module and glow plugs may be activated for a maximum time of 200 seconds. Refer to the following Glow Plug Control chart for a temperature/time comparison of the glow plug relay operation.
In this chart, Pre-Heat and Post-Heat times are mentioned. Pre-Heat is the amount of time the glow plug control circuit is activated when the ignition (key) is switched ON, without the engine running. Post-Heat is the amount of time the glow plug control circuit is activated after the engine is operated.
The Glow Plug lamp
WILL NOT be activated during the post-heat cycle.
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Supporting Vendor and Moderator of LOST05 Jeep Liberty CRD Limited
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