The LCM

[Breadfan]

I wanted to start a thread to try and demystify the LCM - Lighting Control Module. Unfortunately, at the present time, I do not have the required info to demystify, so I'll be looking to the community here to help add input.

The first question is this: What specifically does the LCM do, and what specific systems does it interact with?

For instance, does the LCM simply control the automatic headlights? Does in control all lighting, such as interior lights, dimming, turn signal flashing, hazards, headlights, headlights on w/ wipers, headlights on at dusk, etc.

Does it also control other body-related things such as keyless entry, door keypad, etc. How about any other vehicle functions it controls or interfaces with?

Also, does anyone have a pic of it, either in it's location, or pulled out (or both!). Any pics of an opened LCM?

Finally, does the LCM differ from model to model? Can an '04 LCM be swapped to an '03, and etc. I.E. they aren't tied to PCM codes right?

Given time I may be able to provide much of this info but again right now I don't have it.

This may also help in diagnosing wiper issues people have.

[EbonyMarauder03]

I will look up what it does in full. I can tell you this, it is one expensive turnsignal flasher.

[EbonyMarauder03]

I hope this helps

Principles of Operation

The interior lighting can be separated into two distinct modes of operation: the interior lighting and the demand lighting. The lighting control module (LCM) controls all of the interior lighting in the vehicle, as described in the following text.

The front dome lamps, rear reading lamps, and instrument panel interior lamps can be illuminated either by opening any of the vehicle doors (interior lamp function) or by moving the dimmer switch to the dome lamp position (demand lamp function).

When any door is open, the door ajar switch grounds an input to the LCM which then sends power to the interior lamps. The voltage sent to the interior lamps gradually increases from 0 volts to 12 volts within 0.5 second (± 50 milliseconds), to achieve the theater lighting effect. When the door is closed the door ajar switch breaks the ground to the LCM input which then gradually reduces the power from 12 volts to 0 volts within 5 seconds (± 0.5 second).

When the dimmer switch is moved to the dome lamp position it grounds an input to the LCM which in turn sends 12 volts to the front dome lamps, rear reading lamps, and instrument panel interior lamps. When the dimmer switch is moved away from the dome lamp position, it breaks the ground to the LCM input which then ceases to send power to the front dome lamps, rear reading lamps, and instrument panel interior lamps.

The front map lamps, rear reading lamps, glove compartment lamp, vanity mirror lamp, luggage compartment lamp, and engine compartment lamp (police and natural gas vehicles only) are provided with power by the LCM demand lighting output, and are illuminated when a dedicated switch closes, completing the ground circuit for the appropriate lamp(s). As the LCM provides constant power to the demand lamps, there is no ramp up or ramp down time. The illumination is instantaneous once the appropriate switch is closed.

When a door handle is lifted, or a keypad button is pressed, it grounds an input to the LCM which then illuminates the interior lighting using the theater lighting feature. When the unlock button on a remote keyless entry transmitter is pressed, the DDM sends a pulse signal to the LCM which then illuminates the interior lighting using the theater lighting feature. In either instance the interior lamps will extinguish after the time-out using the theater lighting feature. If a lock button on the remote keyless entry transmitter is pressed, or the ignition is turned to the RUN or ACC position, it will extinguish the interior lamps prior to the end of the time-out.

The battery saver will disrupt power to the interior lamps after 10 minutes, the demand lamps after 30 minutes, and the headlamps after 10 minutes. Turning the ignition switch to the RUN or ACC position will terminate the battery saver feature by disabling the interrupt timers and reinstate power to the lamps.

A reset event will set the interior lamps interrupt timer to zero. The reset events for the interior lamps interrupt timer are: turning on the interior lamps by using the dome lamp switch, opening any door (as detected by the door ajar switches).

A reset event will set the demand lamps interrupt timer to zero. The reset events for the demand lamps interrupt timer are: opening the luggage compartment door or opening any door (as detected by the door ajar switches).

When the panic button on a keyless entry remote transmitter is pressed, the panic alarm will override the interior lamps and headlamps battery saver functions for the duration of the alarm.

On police vehicles only, the dark car feature is a special order option that will override the illuminated entry function. If the feature is activated, the courtesy lamps will not illuminate during entry or exit of the vehicle. However, the interior lamps will still illuminate when switched on from the instrument panel dimmer switch.

The unique police instrument panel harness has an in-line connector for enabling or disabling the dark car feature. The in-line connector (C263) is located behind the glove box. When the connection is made, the dark car signal circuit is routed to ground. The feature is enabled by completing the circuit to ground, and disabled by opening the circuit. To enable or disable the feature, disconnect the battery, disconnect or connect C263, and reconnect the battery.

Lighting Control Module (LCM)

The LCM eliminates the electronic interference and heat associated with the thermoelectric devices used previously. The LCM is a microprocessor- based module that controls several vehicle subsystems. It responds to electrical input signals from various switches, sensors, and external modules.

LCM exterior lighting subsystem functions include:

headlamps with autolamps (if equipped)
turn signal lamps/hazard flasher lamps
cornering lamps
parking lamps
battery saver

[Breadfan]

WOW - This is AWESOME info! This is great! It'll take some time for me digest it, but thanks a bunch for posting that!