E46 Headlight issue

jayok

I have a 325Ci with an intermittent issue in that when I switch on the headlights, sometimes the driver side light doesn't actually come on. I get notification on the dash that the bulb is blown, however, if I turn the lights on/off a few times the light then comes on.

Given that the bulb isn't actually blown and the current sensor for the dash notification is working, I suspect that it is either a cable fault or faulty relay. I can check the cables into the headlight, etc but can anyone tell me where the corresponding relay of this is located in the car? And how to change it?

Thanks.

Seth Brundle

Worst case scenario - light control module?
However, I suspect that its the bulb - is it a cheapo bulb? Sometimes (more so with rear bulbs) cheap bulbs don't provide sufficient resistance and it may think the bulb has blown.

jayok

Hi Kdevitt,

Thanks for the response - the bulb seems fine. When it goes out turning the headlights off and on again simply brings it back on.

Re the LCM - is this some kind of IC logic that contains the amps that act as a traditional relay?

DublinDilbert

jayok wrote: »

Hi Kdevitt,

Thanks for the response - the bulb seems fine. When it goes out turning the headlights off and on again simply brings it back on.

Re the LCM - is this some kind of IC logic that contains the amps that act as a traditional relay?

Yes the LCM is a module which contains the mosfet drivers for the bulb circuits. It also does diagnostics on the bulb for open/short circuit, short to Vbat ect...

It will constantly be doing diagnostics on your bulbs to make sure they are present and working. If it detects a fault it will feed it back to the cluster over the CAN bus.

Firstly i would check and clean up the contacts on each of the bulbs and the sockets which plug into them, some contact cleaner and very light sand paper would do.

If that doesn't work and the wiring is ok, it may well be a fault with the LCM. The bad news is you can't just swap it with one from another car as this acts as the back-up for the mileage in the car. To do a swap you'll need to get someone to re-code the replacement module, not many people can do this.

From memory one of the BMW LCMs used to suffer from some of the heavy solder joints breaking from stress in the unit, i can't remember if it was the E46 LCM, in which case it was just a matter of a few mins with a soldering iorn...

jayok

DublinDilbert wrote: »

If that doesn't work and the wiring is ok, it may well be a fault with the LCM. The bad news is you can't just swap it with one from another car as this acts as the back-up for the mileage in the car. To do a swap you'll need to get someone to re-code the replacement module, not many people can do this.

From memory one of the BMW LCMs used to suffer from some of the heavy solder joints breaking from stress in the unit, i can't remember if it was the E46 LCM, in which case it was just a matter of a few mins with a soldering iorn...

Thanks for the suggestion re the contacts, I'll give them a go.

Re the LCM - Bugger! But I'm handy with a soldering iron so I've no problem checking the module's joints, etc. If it does need a new LCM is this a main dealer visit? What would happen if I did actually plug a LCM from another car into mine? I could avail of those mileage correction services to get the mileage put right.

bonham23

I think the problem with the LCM as described by the poster above is more common on the E39 than the E46. But as he said clean the contacts and maybe replace the bulb with a higher standard one if it was a cheap replacement. The LCM is a costly part alright that factored with an hours labour you'd be looking at €600-€700
An LCM from another car will not work as it needs to be coded to your car.
There are a few indy garages around Dublin that can code them but you'll only save €60-€80 max

Myrddin

its very highly unlikely to be your lcm to be honest. Ive seen this a bunch of times before and can also happen with the bulbs mail dealers use...just replace the bulb with a brand new one, being careful not to touch the bulb glass whilst fitting. Also Ive seen the side light connectors deforming from heat causing a bad contact, which in turn puts the dash bulb warning on so check this too.

rebel.ranter

If it were me I'd shell out he 10 for a new bulb. I noticed isues with cheap rear bulbs giving false readings too (e39 - have xenons up front though).

Seth Brundle

jayok wrote: »

Hi Kdevitt,
...

Wrong K!

EnterNow wrote: »

its very highly unlikely to be your lcm to be honest.

I did say that it was worst case scenario and more likely a bulb!

rebel.ranter wrote: »

If it were me I'd shell out he 10 for a new bulb. I noticed isues with cheap rear bulbs giving false readings too (e39 - have xenons up front though).

Not all have Xenons - mine doesn't!

jayok

kbannon wrote: »

Wrong K!

Sorry kbannon!!

Re the car, the bulbs are not HIDs but standard Halogens. The bulbs used as the Osram Nightbreakers (not exactly cheap) and have been fine the car for the was couple of months. I've a spare set, so I'll check the contacts this weekend a replace them. Problem is the intermittency (sp?) not sure if the thing will fix the problem. Suck it and see I suppose.

spockety

Have you checked the connector block from the light cluster to the loom?

I had a similar problem on my rear lights a couple of months ago, checked the connector block on the cluster (i.e. by separating it) and found half the block had melted away on the inside :eek:

Had to do away with the old connector block and do up a custom one.

JohnCleary

Try swapping the bulbs over and see what happens

jayok

Ok so I gave this a go over the weekend with my multi-meter. Basically when the dash reported blown blub I still had power at the bulb connectors. So either the bulb or the connectors. On further inspection, the contacts to the bulb were covered in some sort of grime. So a quick clean with some white-spirit reconnected the bulb and the problem appears to be have resolved - time will tell.

Cheers for the advice all.