Tail light bulb will not turn on

[Manny G.]

Passenger/Right side tail light, center outer bulb. I've tried different bulb holders, pulled out the headlight, checked all the metal traces, checked for continuity in the circuit,... nothing seems out of place at the rear. I did notice a small burn mark on the contact point on the tail lights metal trace where the BRAKE light below it socket is. I've turned the brake light socket to see if it triggered any reaction to the other light, nothing. I get 4v on the wire at the harness. I've checked for shorts, haven't found any either. This one is really bugging me because its a simple bulb and all of the others light up fine.

I've tried single filament 1156 bulbs
I've tried dual filament 1157 bulbs
I've also tried 5007 5w bulbs, I think these are the ones that are meant to be in there, not sure.. car had mixed dual and single filament bulbs on both sides in those center sockets.

Any input would be very helpful. I've checked the LCM, it was dusty, nothing looked burned or corroded and I can scan it fine with PA soft. I do get frequent rear fog light errors for both tail lights if I disconnect and reconnect the battery.

[SilverIris]

In a 12v circuit like this, you are losing 8v. It is one of two problems here:
1. Voltage Drop (excessive resistance in circuit is burning up voltage)
2. Voltage Divider (shorting to ground, bleeds off voltage proportional to resistance between light and ground)

Grab your multimeter, set it to 200 ohms, and check the tail light 12v+ wire's resistance to ground with the connector unplugged. It should be Infinite ohms. If it reads anything else, you have continuity to ground (shorting out). Let us know what you see.

Travis

[Manny G.]

Ok, so here are my results. I'm even more confused now. For sure I am only seeing 4v on pin 6 Right tail light, all others get 12v. First I tested with the battery connected, then I tested from connector pigtail with battery disconnected, results below with battery disconnected for about 5 seconds on each pin, the ohms slowly crept up in decimals on each.. MM was set to 200ohm range:

Driver/Left
Pin	Type	Description /Signal type 	Connection /Measuring notes	Ohms read 
1	E 	Rear left turn signal indicator 	Light module		10.6
2	E 	Left tail light 			Light module		11
3	E 	Left brake light 			Light module		10.7
4	M 	Ground 					Ground point		4.6 to body
5	E 	Left tail light 			Light module		9.6
6	E 	Inner left tail light 			Light module		11.1
7	-	Left rear fog light 			Light module		n/a
8	-	Not used 		

Passenger/Right				
Pin 	Type 	Description /Signal type 	Connection /Measuring notes	
1	E 	Right tail light 			Light module		8.7
2	E 	Inner right tail light 			Light module		11.8
3	M 	Right rear fog light 			Light module		n/a
4	-	Not used 		
5	E 	Rear left turn signal indicator 	Light module		11.6
6	E 	Right tail light 			Light module		12 < -----------problem bulb
7	E 	Right brake light 			Light module		11.8
8	M 	Ground 					Ground point		4.7 to body

Could the LCM be going bad? I've already started thinking about an LCM IV "upgrade"

[racer2086]

When you stick the multimeter in the connector and then measure to ground, you're measuring through circuitry in the LCM since the LCM is also connected to ground, which is why you're getting those weird readings.

What I would do is use the multimeter to check continuity of the metal traces in the taillight housing to their respective pins and make sure the + and - side of the bulb contacts on the taillight housing measure an open circuit on your multimeter. I would bet there is something wrong with the contacts on the housing or something is shorting it, dropping the voltage to the bulb. Also, Where the bulb socket makes contact can burn or pit, leading to inadequate contact to pass voltage for the bulb.

[SilverIris]

Racer2086, that would explain some of the resistance readings tied to every light, but it's still a matter of "one of these things is not like the others". Either way, there is still excess resistance to 12v+ (caused by corrosion probably) or insufficient resistance to ground (shorting)

I would trace the circuit back to the LCM connector and check your voltages there. If both tail light pins read normal at the LCM but the one in question gets goofy at the tail light connector, you have a wiring issue. If it reads weird at the LCM, then the LCM is suspect.

[Manny G.]

When you stick the multimeter in the connector and then measure to ground, you're measuring through circuitry in the LCM since the LCM is also connected to ground, which is why you're getting those weird readings.

What I would do is use the multimeter to check continuity of the metal traces in the taillight housing to their respective pins and make sure the + and - side of the bulb contacts on the taillight housing measure an open circuit on your multimeter. I would bet there is something wrong with the contacts on the housing or something is shorting it, dropping the voltage to the bulb. Also, Where the bulb socket makes contact can burn or pit, leading to inadequate contact to pass voltage for the bulb.

I did originally check the traces, they were all fine. Yeah, the ohm readings I got lead me to eventually realize something might be up with the LCM. The voltage drop is on the harness pigtail without even being connected to the light housing.

Racer2086, that would explain some of the resistance readings tied to every light, but it's still a matter of "one of these things is not like the others". Either way, there is still excess resistance to 12v+ (caused by corrosion probably) or insufficient resistance to ground (shorting)

I would trace the circuit back to the LCM connector and check your voltages there. If both tail light pins read normal at the LCM but the one in question gets goofy at the tail light connector, you have a wiring issue. If it reads weird at the LCM, then the LCM is suspect.

That's exactly what I was thinking of trying tomorrow.. from the LCM side check for a short I'm also going to try applying external 12v to the harness from the LCM side to see if the bulb lights up... that should also tell me if there is a short in the wires. TIS says its pin 17 on the 54-pin connector of the LCM.. interestingly enough, it's the only pin on that harness for the tail lights... all other tail light wires are on the 15-pin connectors.

I'll reply back with results soon

[Manny G.]

Finally fixed this.

Issue was with the old LCM III module. I changed it for a 4b version, didn't even code it yet and the light is already working.

[alexisonfire]

Finally fixed this.

Issue was with the old LCM III module. I changed it for a 4b version, didn't even code it yet and the light is already working.

4b?
And jeez didnt know youve been here since 2001! mad respect.

[Manny G.]

4b?
And jeez didnt know youve been here since 2001! mad respect.

Yeah I was actually on from 2000 but in Sept. 2001 the old Admin Bob///M3 banned a ton of misfits that were invading the forum from DTMPower (if you remember that, then consider yourself truly "Old School").


The LCM 4b is the upgraded version of the LCM module. The LCM 4 came on the later years of the E53 X5, but he 4B version came on the last few E39s. The E39 LCM is more compatible than the E53 one from what' Ive read on other threads. The one I ordered happened to come from a European version 2003 530i Touring... my first error when plugging it in was about self leveling suspension not working. Coding sorted it out for me.

For me it was as simple as swapping the module, coding the VIN to it with PA Soft, then coding the module with NCSExpert. The module comes up as LCM.C24 which is the last one compatible with the E38.

If searching ebay for it, it should be LCM-4b Man. LWR , part number is 61356961141. I've tried digging up more threads on this but either Im using the wrong search terms or there just isnt much detail out about this. LCM 4 adds a few extra features such as Follow Me Home lighting.. maybe a few others Im forgetting

61356961141 is the part for the 4B module

The one that came out of the car, LCM III , original factory part, ended in "8 386 208" , i think the complete part number is 61358386208