SRS Warning lamp coming on with Headlamps?

[JC220]

Hi all, my 1992 500E is putting on the red SRS warning Lamp in the Instrument cluster when the headlamps are turned on. (High beam and Low Beam both) The SRS lamp stays lit constant with the headlamps on and goes out as soon as the headlamps are switched off again.


I have the car’s first Northern Ireland MOT test is coming up within a couple of weeks. It’s very strict unlike the English MOT system. Any warning lamps coming on at all during the test is an instant fail – so I must attend to this problem pretty urgently. They specifically look for the Warning Lamp functions in NI- like this news article

http://www.bbc.co.uk/news/uk-northern-ireland-17908259



Has anyone else experienced this before? Where should I start looking for where the problem lies?


The car has the updated Ceramic Fuses and Eco junk replaced with new MB harnesses.


It could be linked not just to the headlamps – but the interior illumination circuit also. It’s bizarre & annoying though! I do have Star but don’t know what use that will be for the SRS fault.


Any hints or tips are appreciated

 

[nocfn]

Consider a new headlight switch. They are not that costly (stay away from Chinese junk) and like the ignition switch, that rotary sucker gets a lot of stuff going on. While I cannot tell what may be specific, if it is the original switch, change it out as they do wear out. If you cannot get that to go in time, you could temporarily fudge and remove the cluster, then the bulb from its holder and get inspected.

 

[r44raven]

I don't know the detail of a NI MOT test, but here on the mainland UK, as I understand it, the rules about the SRS light are as follows:-

When the ignition is switched on, the SRS lamp must illuminate for a few seconds, and then go off. I believe this is part of an SRS "self-check" procedure? In this situation, taking the bulb out of the SRS bulb holder prior to the test wouldn't work; the test would be a fail because the light didn't illuminate on start-up.

I think you should check if the same applies in NI? Your local MOT station should be able to confirm/otherwise?

 

[Klink]

Do you have any kind of aftermarket lighting installed, particularly any kind of HID/Xenon or LED lamps?

 

[gsxr]

Pull the cluster and make sure the wires to the bulbs on the tach/clock are in the correct order. The wires should be numbered. My guess would be something got switched. The SRS system should have almost no connections with the rest of the electrical system.

 

[Klink]

I suspect euro vehicles are wired the same way, but at least on USA version vehicles, a quick check for that that condition would be to turn the ignition switch to the "accessory on" position, not the "engine on" position. All of the warning lights should be off except for the SRS lamp, which should remain on for a short period of time, and then extinguish. All of the other warning lamps should remain off during this period of time. If a lamp behind some other icon lens illuminates, that bulb is actually the SRS lamp, and then yes, it and other malfunction indicator bulb holders are installed in the wrong holes in the back of the cluster. This test works because the SRS is the only one of those systems that is energized with the key in the accessory and run positions.

 

[JC220]

Dave, Klink you guys just hit the nail on the head!!




I often wondered why the bulb warning lamp came on & went off after a couple of seconds with the ignition at the first stop. Thought it was just the car’s way of telling you the ignition was at accessory or something.


I have never had the cluster out before – so someone else in the past has inadvertently swapped the SRS & Failed lamp warning bulbs


It makes sense- what is actually happening when the headlamps are switched on is the Blown Bulb warning is coming on. Then going out again when the Headlamps are switched off. So I need to check / clean all the bulb connections & see what’s going on. After I swap the warning lamps in the cluster around of course!


I can deal with that – didn’t know what to do with the SRS lamp.

 

[JC220]

I don't know the detail of a NI MOT test, but here on the mainland UK, as I understand it, the rules about the SRS light are as follows:-

When the ignition is switched on, the SRS lamp must illuminate for a few seconds, and then go off. I believe this is part of an SRS "self-check" procedure? In this situation, taking the bulb out of the SRS bulb holder prior to the test wouldn't work; the test would be a fail because the light didn't illuminate on start-up.

I think you should check if the same applies in NI? Your local MOT station should be able to confirm/otherwise?

Well the way it works here is they will have the headlamps on to check the beam alignment etc on the Headlamps. If any warning lamp comes on at any time they will fail it for sure.

Basically the MOT staff here are all government personnel and more often than not it feels like they are LOOKING for a reason to fail a car. Especially one that’s not been tested in Northern Ireland before- they will go through it with a fine tooth comb for sure.



As for the Bulb failure warning it comes on with the sidelights –even though there are no blown bulbs.

So now I am going to order up some quality new bulbs such as Osram and renew the Tail lamp bulbs, Licence Plate bulbs & the Sidelamps themselves. And make sure the holders are all clean & corrosion free.

Question – would the interior instrument illumination bulbs also be able to trigger the Bulb Failure lamp?

Again – I have already replaced the blown bulbs in the interior but maybe I’ll need to take a closer look if the new ‘outside’ lamps don’t make the warning lamp extinguish

 

[gsxr]

As for the Bulb failure warning it comes on with the sidelights –even though there are no blown bulbs. So now I am going to order up some quality new bulbs such as Osram and renew the Tail lamp bulbs, Licence Plate bulbs & the Sidelamps themselves. And make sure the holders are all clean & corrosion free.

Question – would the interior instrument illumination bulbs also be able to trigger the Bulb Failure lamp?

Nope, interior illumination bulbs are not monitored. Don't forget to check the license plate bulbs. If the warning light comes on when you ONLY turn the headlight switch one click to the marker/side lights, that really narrows it down.

 

[JC220]

Yes that's correct Dave- it only comes on every time I turn the side lamps on. And goes out as soon as I turn the side lamps off again.

So I have ordered boxes of 10 Osram bulbs for each bulb type. Side lamps, tail lamps + license plate festoons. All stock bulb types.

That's good to know the interior lamps can't trigger it.

I'll replace all bulbs on the sidelamp circuit and see how it goes then

Thanks again everyone for your help

 

[JC220]

So the annual inspection is now moved forward to this Saturday. (Since my W211 ‘s cluster is away to BBA Reman – I have no other car!) I am going out soon to start troubleshooting the fused bulb warning lamp problem.


One other thing – the warning buzzer for the headlamps being left on comes on all the time if the door is opened. Ie; even with the Ignition on and the car running – if you open the drivers door with the headlamps on it buzzes constant. Hugely annoying! I think it’s only supposed to come on if the ignition is off, headlamps on & the door is opened.


I presume the buzzer is relay controlled somewhere? I cannot locate it on wiring diagrams- so not sure where to look. That could be linked to the warning lamp coming on all the time – if a module / relay has failed maybe so I’m aiming to resolve that issue also just to rule it out

 

[gsxr]

Are you sure it's the headlamp buzzer, and not a seatbelt reminder? You can disable the seatbelt reminder by disconnecting the wire connector under the driver seat.

 

[JC220]

Hi Dave – yes its the Headlamp buzzer I’m pretty sure. Also when I turn the headlamps off it doesn’t Buzz. I don't think it has a seatbelt buzzer.


But the problem is when for example the MOT centre is testing the headlamps they are left on and I swap seats with the Inspector. So the Buzzer will go mad. They can’t fail me on that I’m sure but it’s just irritating and embarrassing!


Plus I do wonder if a fault lies somewhere which is ‘helping’ trigger the warning lamp. Maybe someone ‘fixed’ the buzzer by tapping into a headlamp wire – thus triggering the blasted warning lamp.


I have all the new bulbs – except the front sidelamp ones so I’ll install those tomorrow night but I’m not sure that’ll actually cure the warning lamp coming on. Last ditch resort will be to fit a relay on a temporary basis to disable the warning lamp bulb & get the car through the test

 

[JC220]

I got a rare couple of hours spare time tonight so went out & did the following-

Renewed both License plate illumination bulbs. This included very thorough cleaning of all the terminals / holders and extra zip ties to keep really strong connections on the tail lamp cluster bushbars. New High quality exact OE spec bulbs fitted.

Although the bulbs actually look brighter in there now – warning lamp still on.

Swapped out the Bulb monitoring Module for one from my E36. Part number of the E500 unit was 126 545 03 32. E36 item was 126 545 00 32. Pins were all the exact same.

No good- warning lamp behaves exactly as before. (Comes on as soon as the sidelamps are switched on)

Moved on to the front headlamps. Found that the driver’s side plug was badly corroded. Cleaned that up as best I could. Inside both front headlamps the sidelamp bulbs were also corroded. The sidelamps are the only new bulbs that have not arrived yet. So I cleaned the old ones and put them back in until tomorrow night.

Warning lamp still on.


Ahead of adjusting the beam pattern for the MOT I thought I would take a quick check of the beam pattern (In general) –



One headlamp looks duller than the other – wtf? Weak earth – I don’t know. I'm fairly certain now the car has E500 Headlamp housings - with stock w124 lenses fitted. (To correct the beam pattern for UK roads - but they're doing a crap job)


I guess I’ll fit all new bulbs to both headlamps tomorrow night and see how it is after that. I'm all ears for any other suggestions


The new E500 headlamps will come very soon but I need to limp it through MOT with these ones in 72 hours!

 

[TerryA]

JC,

You mentioned the headlight buzzer but I don't see where it was fixed. I'm no brain when it comes to electronics but could the headlight buzzer be shorting out somehow and causing the SRS warning light to stay on? The electrics do funny things when something is shorting out. The contact points in the buzzer relay could be welded together.

I had a problem a while back where my seatbelt warning light kept flashing all doors closed and seatbelts on. I flashed like that for about a week night and day. Some how it corrected itself with no help from me. I think the points in the relay just broke apart and went back to normal mode.

Just a guess. The Northern Europe climate must be hell on your cars. I hope you find your problem.

Take Care & Good Luck

 

[JC220]

Hi Terry,


I did find a bad headlamp bulb on the dip beam so I think that explains the duller headlamp. But doesn’t explain why the warning lamp comes on with the sidelights.


Yes I agree that next I must investigate why the buzzer comes on with the Ignition on & the door open – maybe the system is very sensitive and it’s detecting that abnormal current somewhere. So on Saturday morning I will make the buzzer stay on – locate it and trace the wiring back until I find what controls it. I also have a spare headlamp switch to hand so I’ll try swapping that out.

 

[JC220]

I went and looked out one of my spare clusters. Connection the wires like this makes the headlamp buzzer sound (It’s in the cluster!)




So since this part looks to match the 500E’s cluster I will swap this part out & see if it makes any difference. It has a relay soldered on the back – presumably for the headlamp buzzer function. If the signals to the cluster are AOK then it has to be it!

 

[gsxr]

I've never seen a gauge cluster with a relay soldered to the back - I wonder what it is for. I think the headlight buzzer is located behind the cluster up against the firewall, under some insulation?

 

[nocfn]

It is on the 126 that is, and it gets failures too.(up under dash near column)

 

[JC220]

Well my new MB hooks arrived so I pulled the 500E cluster – see the pics it’s exactly like that other spare I had.



Must be a Euro thing then?

For sure that grey part is the headlamp buzzer – I tested it with the cluster still plugged in.




Another very useful test was plugging the spare part in. The headlamp buzzer still sounds with the ignition ON and the door opened.


So the only thing I can say now is there is a problem with the circuit somewhere regarding the door opening / warning lamp system. I will figure it out but for right now she’s likely going to the test as is with time constraints! Maybe I'll do a 40ft burnout at the door on the way in & they won't see the warning lamp

 

[gsxr]

Must be a Europe/Japan-only thing on the 124-542-44-01 gauge cluster.

USA models use cluster 124-542-45-01 which do not have the black cube relay on the back of the F/O/T gauge.