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!

[xopher]

I'm the next contestant on Your Headlights Won't Stay On At Night.

After figuring out where the LCM is and how to bang on it with an Altoids tin, I determined that my intermittent headlights is due to the LCM. I am familiar with the external rely mod developed on crownvic.net (http://www.crownvic.net/ubbthreads/u...871445&fpart=1). I am considering doing this, but I was also considering replacing the whole LCM myself, as any dealership will charge ~$600-~$800. Buying the LCM alone might cost only $275 (http://www.trademotion.com/partlocat...&siteid=214944). Before I try the advanced board repair option, I was considering getting a used LCM and swapping it in, which leads me to Breadfan's unanswered question, and the reason I chose this thread in particular to bump:

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

1) Is the LCM from a 2003 MM the same as a 2004 MM?
2) Is the LCM from a 20XX Crown Vic or Grand Marquis the same as a 2003 MM?

[fastblackmerc]

I'm the next contestant on Your Headlights Won't Stay On At Night.

After figuring out where the LCM is and how to bang on it with an Altoids tin, I determined that my intermittent headlights is due to the LCM. I am familiar with the external rely mod developed on crownvic.net (http://www.crownvic.net/ubbthreads/u...871445&fpart=1). I am considering doing this, but I was also considering replacing the whole LCM myself, as any dealership will charge ~$600-~$800. Buying the LCM alone might cost only $275 (http://www.trademotion.com/partlocat...&siteid=214944). Before I try the advanced board repair option, I was considering getting a used LCM and swapping it in, which leads me to Breadfan's unanswered question, and the reason I chose this thread in particular to bump:

1) Is the LCM from a 2003 MM the same as a 2004 MM?
2) Is the LCM from a 20XX Crown Vic or Grand Marquis the same as a 2003 MM?

I believe the LCM's are different between some years and models.

Send me your LCM and I'll put an external relay on it for $25.00. Once installed will look like this.

[fastblackmerc]

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.

The LCM is located right behind and above the OBDI port. Remove a few screws and connectors and you can finagle it out.

Pics of an opened LCM

[SC Cheesehead]

1) Is the LCM from a 2003 MM the same as a 2004 MM?
2) Is the LCM from a 20XX Crown Vic or Grand Marquis the same as a 2003 MM?

I'll chime in now, and will follow up with some additional info when I get home this evening.

I recently swapped out my LCM with one from a 2004 GM (tip of the hat to RoyLPita for supplying part numbers). The unit works well, but it is a different p/n than the OEM that was in the car. I bought the replacement unit from a salvage yard, but I found out Panther LCMs are a hot item. I contacted a bunch of salvage yards around the country, and those that had '03-'04 Panthers had already sold the LCM's out of them. In fact, one yard up in VA had 2 MM's, but the LCMs out of both were gone. Depending on the particular yard, expect to pay between $50 and $100 (still a whole lot cheaper than a new OEM)

The relay change out will fix your problem, but IMO unless you go with the HD relay, you may have a re-occuring issue. I did a direct replacement with a factory spec relay that I got through Mouser Electronics and that fixed the problem immediately. However, this summer, started having issues again, and the unit failed completely during Marauderville last month. A word on the failure: Banging on the unit will work in most cases and will cause the headlights to come on, but as I found out the hard way, there are a limited number of "bangs" that you can perform before the relay craps out for good. So word of advice. The "bang fix" should be used like a donut spare tire, sparingly...

Oh, one last thing. Consider taking fastblackmerc up on his offer. His retrofit is top-notch, and the set-up he uses to re-locate the HD relay gives you easy access to it without removal of the whole LCM.

[GordonB]

Back to the Orig. Question: Is the LCM for an '03 MM the same as the one for an '04 MM? Not asking about CV of GM, just MMs. Appreciate edumicated feedback.

I now have an '03 MM LCM that needs a new HD relay. Dealer didn't have to ship the old one back under warranty so I got it as a spare to work on.
GordonB

[justbob]

Many thanks goes out to all of you! My headlights failed to come on the other night for a couple seconds, I heard a click and then they came on. It did this every time I turned them off and on again. But it only did this one night last week.

[SC Cheesehead]

The LCM that was originally in my car was a 3W7T-13C588-AH. Fastblackmerc did the HD relay retrofit on this one, and I'll swap with out with the current replacement unit if/when I have any problems with the "new" one.

I replaced it with a 4W7Z-13C788-BB that came out of a 2004 Grand Marquis.

I also got the following info from RoyLPita. In addition to the 4W7Z-13C788-BB, a 4W7Z-13C788-BC will work, and these additional p/n's should also be compatable: 3W7Z-13C788-AA, 3W7Z-13C788-AH, 3W7Z-13C788-BA, 4W7Z-13C788-AB, 4W7Z-13C788-BC, or 4W7Z-13C788-BA.

[xopher]

edit: nevermind for now

[xopher]

Sorry about the unintentional bump there.

Thanks again for all of the helpful advice here. I almost got the LCM out last night, removing the cosmetic plastic cover, removing the bolts that hold the LCM in its bracket, and unplugged the two gray cables going into the fore-side of the LCM. However, when I removed these two, I was then able to see a third plug, a black plug seating into a white socket. The white socket is the one I'm pointing to with a blue arrow here:



I had to stop working on it because I was too cold and too late, but I couldn't get the black plug out, and I couldn't find any clips holding it in place. It was pretty cramped quarters and I couldn't even get a pliers on it. I hope I don't have to start disconnecting everything down there to get this thing out. Am I missing something? Any tips?

[justbob]

If you take out one of the two mounting bracket screws and loosen the other, you can actually "tip" the bracket and slide the LCM out with ease, then disconnect the wires now that you can see them.

Just move the LCM back a little to access the first screw and remove that one (sideways, screwing towards the trans tunnel.)

[fastblackmerc]

Sorry about the unintentional bump there.

Thanks again for all of the helpful advice here. I almost got the LCM out last night, removing the cosmetic plastic cover, removing the bolts that hold the LCM in its bracket, and unplugged the two gray cables going into the fore-side of the LCM. However, when I removed these two, I was then able to see a third plug, a black plug seating into a white socket. The white socket is the one I'm pointing to with a blue arrow here:



I had to stop working on it because I was too cold and too late, but I couldn't get the black plug out, and I couldn't find any clips holding it in place. It was pretty cramped quarters and I couldn't even get a pliers on it. I hope I don't have to start disconnecting everything down there to get this thing out. Am I missing something? Any tips?

Disconnect the 2 bottom connectors (usually black, brown or dark grey), disconnect the top connector (usually white), unscrew the 2 gold colored screws (7mm or 8mm) and wiggle out the LCM.