Tail light gremlin please help

taosx5 · #1 08-12-2012, 10:22 PM

I have searched many threads and can't find anyone with the same exact issue. Hoping some X5 guru can offer some good advice. Here is the deal on wife's 03 4.4 X5. She first started getting intermittently for several weeks a "check brake lights" then she started getting another intermittent "check rear light". Nothing was wrong with the lights everything seemed to work fine, then her left rear blinker on the dash started rappidly flashing but the tail flasher would not come on. I just learned of all of this and started trouble shooting.

Here is what I have done.
-The left blinker light on dash flashes rapidly, the front blinker does the same but the read does not come on at all. Everything on right side works fine

- I first changed all three bulbs on left side which none of them appeard to be burned out and inspected for any corrosion or anything mentioned in the threads. There was no corrosion at all.

- Then I switched all three blulb and sockets one at a time from the right to the left. The two lower ones (brake and tail light) from the left worked on the right side but none of them from the right side worked on the left side. The top bulb and socket (the blinker) from the left one does not work on the right side. I felt this might be the problem but what can go wrong with the socket? There appears to be good contact with the bulb and within the slot it snaps into.

-Emergency flasher works on both fronts and right rear but not left.

I felt the left bllinker socket is the problem but then why does the working one (from the right side) not work when plugged into the left side?

Could it be a bad relay? If so does anyone know where the relay is located and anyone know the part # so I can replace myself?

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mrbmwx5 · #2 08-12-2012, 11:17 PM

Good time to upgrade them to LED's tail lights.Your lights housing is bad ( rust/ corrosion)
or hardwire the socket with new wires to the wiring harness,or buy a repair kit from mercedes benz dealer.

taosx5 · #3 08-12-2012, 11:24 PM

Thanks for the reply.

Where is the corrosion, nothing that I can see has any evidence of corrosion? Is it the enire tail light housing or is it internal components?

I have read a little on LED changes but can you elaborate on what needs to be done ie part numbers, cost, etc? Can you just change the rears without messing with the fronts?

Thanks for any and all shared wisdom.

SlickGT1 · #4 08-12-2012, 11:38 PM

Take out the tail. You will see where the corrosion is right away. When you see it, come back here and search for the DIY.

taosx5 · #5 08-13-2012, 12:10 AM

SlickGT1, what do you mean by the "tail"? Does this mean pull out the whole light assembly? Thanks in advance for your reply.

TerminatorX5 · #6 08-13-2012, 12:31 AM

the tail light assembly is held to the car's body by three 10mm nuts (could be 8mm, but I think it is 10mm). Once you remove the nuts, one at the time, and make sure you do not drop them into the fender well on the inside, as then, you will have to pull all of your electrnocs out in order to fish out the nut, then you take the assembly out.

The assembly slides out, along side the main car axis, you will see, it comes off and goes back on just one way. The assembly might be stuck to the body by the means of debris, that has collected over the years, or just by simply, rubber sticking to the body... Just wiggle it out. when you pull the body out, you will see that the openings for the light bulb sockets have their metal portions, and those are the ones that are corroded. The LCM tell the driver that one of the turn signals is out by rapidly flashing the turn signal, and also by displaying a message on the high cluster.

clean the metal portion of the contact assemblies with a fine sandpaper, but keep in mind, you don't want the dust and debris end up inside the lens. wipe it off with alcohol wipe, not just wet napkin or whatnot...

the LCM checks the resistance of the circuitry when the lights are off, by sending a series of fast pulses to every light socket on the list, and reads the amperage of the circuit, thus checking for resistance of the line. If the line is broken, as in a burnt light bulb, there will be no current, and the resistance is infinite, so the light circuit is defective... But here lies the BMW engineering at its best - the LCM not only measures for dry contact, yes or no, it also measures for the current itself, therefore, if the line shows higher resistance, as if corroded contacts would, the LCM tries to compensate for it by sending higher amperage to that light bulb, which just extends the agony of the light bulb, and the higher amperage kills the light bulb rather sooner or later...
That explains, why sometimes we get the computer warning that the light is out, but everything is working - all it means, that the light WILL be out soon...

sorry for long winded explanation... lol...

taosx5 · #7 08-13-2012, 09:14 AM

Terminator, thanks, I appreciate and sort of understand what you have explained. I know very little about electronics but yours is a great expanation. I know about the three little nuts you talk about. I suspected that is what held the assembly in. And I appreciate the warning about not dropping one of them. On an 840 I had I was changing a bulb which was about a 5 min job and I dropped a similar nut that took about an hour to figure out how to find it and then fish it out.

tmv · #8 08-13-2012, 09:24 AM

Upgrade to LED taillights. The problem would never come back

TerminatorX5 · #9 08-13-2012, 09:25 AM

TerminatorX5 · #10 08-13-2012, 10:14 AM

If you decide to go the LED route, there are few things to consider, aside from the aesthetics of the look...

Since the Light Emitting Diodes (LEDs) have a much faster response time than the regular incandecsent light bulbs, those Pulse Modulation Waves (PMW) that the LCM sends out actually light up the diodes which results in flickering of the LEDs, that so many people have reported. Also, since the resistance of the diode might not match that of the light bulb, the LCM may incorrectly think that the circuit is broken (diode is like a water valve, lets electricity one way due to low resistance, and blocks electricity going the other way, due to super high resistance).

When you get the LED tail light, check to see if the unit is equipped with the "code cancelation" circuit, essentially a bypass circuit that fools the LCM into thinking that the regular bulb is there. Another option would be to turn OFF the Cold Monitoring of the rear tail light, brake light and the turn signal lights in the coding of the car, that can be achieved by a full version of the NavCoder or a NCSExpert software. When the Cold Monitoring is OFF, the LCM simply does not bother checking the circuit at all, thus, no flickering, and no "light out" message...

In the NCSExpert programming, there is also a line for LED taillights but I am not sure what that line does, once activated.

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