DIY: LBF Fix w/o disabling CCM easy & free!

[dhoeffner]

This is for E36, the CCM function on later models is different.
I don't like seeing the LBF msg and do not want to disable my check control function. Nor do I want to add a current load to the circuit as those purchased modules do, this is just a wasteful current drain.

The fix is pretty easy and only takes 30min or so, best of all its free!
The CCM (check control module) system works by putting a very low resistance resistor in series with each headlight circuit, then measures the voltage drop across it. If the voltage drop is too small it thinks the bulb is open circuit. The tungsten 55W bulbs draw 4.5A, HID 35W lights draw only 3.0A (steady state), therefore the CCM sees less current and triggers the low beam failure msg.

The way around this is to increase the series resistor in the CCM module so you get a slightly higher voltage drop and the CCM will not trigger an error. Now some will say increased resistance is bad, let me tell you the resistance increase is so small its its negligible, the series resistor is 0.005 ohms and it gets increased to ~0.006 ohms which is insignificant in terms of power delivery to the lights.

Tools: DMM (digital multi meter), small wire cutter.
First get to the CCM module, remove the under dash panel on the drivers side. The CCM is above the dead pedal, its held in with 2 thumb screws, you only need to loosen the back one (closer to the engine), and remove the one closer to the back of the car. Its about 3”x5” in size. It has 2 big wire connectors on it, one black, one white, no need to remove the connectors. The top cover pops off be squeezing 4 snap clips.

See basic schematic below. The CCM measures voltage drop between point A and B. I think it is looking for >0.016V (16mV). Stock drop is ~0.023V, with HID it is about 0.016V and therefore sometimes triggers the LBF.



Here is the CCM opened up and unadulterated.


The metal strips on the board are very low value resistors. The ones labeled RM9 and RM10 are the ones for the headlights.
Now with HID lights on, measure the voltage across those resistors. Be careful to not be shorting things together, it is a live circuit and could be easily destroyed!

Now turn off the key, take cutters and trim away metal near the center as I have as seen in the pic. The metal is a bit tough to cut. Do this with the key and headlights off and be careful not to cut metal strip into two pieces!


Be conservative, then measure voltage drop, it should increase. Trim away until the voltage drop is ~0.019V to 0.023V across the end sides of each resistor and then you are done! That’s it, put it back together and enjoy getting no error messages!

[Phillips0417]

Wow! How did you figure this out? Luckily when I had my E36 and installed HID's, I wasn't plagued with the infamous LBF. Good job!

[themadrussian]

This seems more complicated than cutting the wires, but better than disabling Check Control through the OBC. However, this is definitely a "better" fix.

Kudos!

[acastillo]

thank you for sharing. I may just have to do this. How different would the calculations be for 55w ballasts? I'm not sure how much more they draw than 35w.

[dhoeffner]

thank you for sharing. I may just have to do this. How different would the calculations be for 55w ballasts? I'm not sure how much more they draw than 35w.

Are you getting LBF with 55W HIDs? I'm not sure how much they draw either, if you could let us know that'd be great. I'd think if the HID is 55w then there should be no LBF. Use an ammeter, pull the head light fuse, and hook the leads up where the fuse was. I know on my 35W the current draw was 3.0A (after 15 seconds or so, and higher initially). I'd be intersted to know what the draw is on a 55W set up.

The procedure should be the same, measure the drop across those metal resistors when the lights are on and look for >19mV. Unless of course the CCM is fubar.

[acastillo]

I had Prolumen 35w ballasts on the car for 3yrs, then the LBF showed up. I switched to 55w Apexcone ballasts, and then to 55W DDM slim ballasts...neither eliminated the LBF.

I will measure the current draw tomorrow if I have time. However, DDM has this on their site for both 35/55w slim ballasts: "Fully digital, draws less than 6 amps at start up and 3.4 amps at normal operating temperature"

[dhoeffner]

Well 3.4A could set off the LBF. It is expecting ~4.4A through the headlights. I am sure there is a good amount of variation in the CCM sensing circuit since it does not need to have much precision.

I had 35W DDM balast that drew 3.0 amps and did not trigger LBF, then I got their 35W "Raptor" balast and would get LBF after 5-30 minutes. These also measured 3.0A. There may be some variation bewteen what my DMM shows and any actual transients that would explain the LBF on the raptor and not the DDM.

[Tomek]

Great writeup!

I'm getting LBF on stock headlights, have 55w bulbs, measured current draw is 4.0A, voltage at low beam fuse is 14V with engine running. According to your findings this should not trigger the LBF warning.
Can this be because of ridiculous fuse values? (25A and 30A, previous owner put those for HIDs probably).

Also, is it possible that on euro-spec the CCM checks the beam throw motors as well?

[dhoeffner]

Great writeup!

I'm getting LBF on stock headlights, have 55w bulbs, measured current draw is 4.0A, voltage at low beam fuse is 14V with engine running. According to your findings this should not trigger the LBF warning.
Can this be because of ridiculous fuse values? (25A and 30A, previous owner put those for HIDs probably).

Also, is it possible that on euro-spec the CCM checks the beam throw motors as well?

I doubt the fuse size is affecting it. Possibly the motor, I have no idea. Voltage and current are good. Are you sure all your connections are tight? I would double check these including the light switch (perhaps by checking the voltage to the headlight relay), there could be a intermittent condition that is not perceptible as the lights going out. Also look at the filaments, these can be intermittent as well as they age.

I would also just measure the voltage across these two resistors in the CCM but not cut.

[Tomek]

Is it safe to rule out the motors? ETM diagram doesn't include them as going thru CCM.
Filaments should be OK, I've put new bulbs few days ago (55W Hellas or Philips).

I'll double check the voltage across the whole circuit then. Thanks.

[Hot Rides]

awesome fix

[adstock]

I'm going to try this once i get HIDs. Thank you.

[LuvMy328is]

Good info, I too had HID's for many years then one day, BAM LBF ftl
~Phil

[addnon]

Why do some cars get the LBF but others do not? Specifically within just the E36 gen.

[Brent 930]

Those aren't resistors, they're shunts. What you did is change the calibration/spec. of the shunt that reports the current.

The best way is just cut the traces to isolate the shunts from feeding back. It's not like you won't know when a headlight goes out.

Either way A+ for effort.

[dhoeffner]

Those aren't resistors, they're shunts. What you did is change the calibration/spec. of the shunt that reports the current.

The best way is just cut the traces to isolate the shunts from feeding back. It's not like you won't know when a headlight goes out.

Either way A+ for effort.

Thanks. The term shunt may be the more correct term, but resistance is easier to relate to IMO since many know V=IxR. Its the same principle either way.

From http://www.rc-electronics-usa.com/current-shunt.html: "So by inserting a current shunt into a circuit whose current you want to measure your can find the current by measuring the voltage drop across the shunt. Then knowing the resistance of the current shunt you can calculate the current using Ohm's law arranged as I = V ÷ R."

Yes the shunt's resistance value was increased with the trim. This essentially tricks the monitoring circuit into thinking there is enough current flow and the bulbs are OK. It is easy enough to know when your headlight is out although I like to keep everything functioning.

Why do some cars get the LBF but others do not? Specifically within just the E36 gen.

I believe it is just due to variation in the ballast and the CCM circuitry.
I had two 35W HID balast, one no LBF, the other had it. Both showed 3.0A draw by the ballast. I think I was just on the hairy edge with both of them.

[adamnur]

Interesting--never seen this fix before. I'd try it, but I'm a little apprehensive when it comes to modifying things like this. Perhaps I'll try it after summer when I have to turn on my lowbeams more often

[Brent 930]

OP, you did well. Shunts are calibrated and it seems these shunts get out of cal. all the time, thus causing the LBF. Shunts are typically calibrated vs. a known standard for accuracy.

Resistance goes down, current goes up.

Resistance goes up, current goes down.

In this case voltage stays the same, but the power will change.

[Dantesboyz]

i have 55w hids on the low beams and 35w hids in the fogs and i only get lbf if i immediately turn them on after i start the car. if i just wait 5-10 seconds after starting the car and i never have a problem. otherwise its nice to know theres other people out there that understand shunts across resistance bridges. nice work gentleman.

[firedancer414]

Hi, I don't mean to be negative, or go around bringing threads back from the dead, but this did not work for me. My CC module was very similar looking, but not exactly the same. I located the 9 + 10 modules and trimmed them down to almost nothing, to no effect.

I eventually had to go through the usual clipping of the yellow wires in the white harness and connect gray-green and blue-red like everyone else. I guess that it doesn't really matter to me, since I just ignore the warning anyway. It doesn't bother me much, but everyone in my car always gives me crap for the LBF. Anyway, all fixed now!

[ryanmkincaid]

Has anyone one besides the OP tried this and had it work? If so, why isn't this a sticky?

[HarryN]

I think it's because it doesn't always work. My friend tried this fix on his car recently since has the same LBF error as I do. We measured the voltage as we were cutting, per the instructions, and no avail. We then switched to 55W low beam bulbs, no avail. Then we replaced the relays, fuses, nothing. Even went as far as disassembling the wires that connect to the bulbs and re-soldering the connections back to their original plugs using the "newer wire" portion of the wire, nothing. Same error.

Then we tried to change the light switch, nothing. We tried unplugging and re-plugging the CCM in, and for a brief minute, NO LBF ERROR!!! But as soon as we started driving for a while, it popped right back up and even caused a Brake Light Circuit Failure as well. We turned off the lights (this was done during the day time) the brake light circuit failure went away but the LBF was still there. We thought it might have been the alternator, but it was measure at 14.3V while the car was running, so that cancelled that theory out.

I think at this point, it would be better to just get a new CCM. They are expensive at $230 a pop (part number 61358353098), but if people still rely on their CCM to give pertinent data on any errors, this would be the way to go without having to splice any wires or whatever.

I think this will be my course of action as well. This thing is getting on my nerves.

[lotusing]

I don't have an e36 but an e30 with this exact issue and it driving me crazy. I too don't want to pull the error bulb or alter the ccm ether but I have tried different resisters but to no avail. Would you have and idea as to shut my light off as well?

[dwonda]

Has anyone looked into doing something similar to not disable the messages for the license plate lights, tail lights, and brake lights, but to just have it "calibrated" to LED bulb replacements?