Electrics: S40 Dodgy Headlight

[2009rovert]

I wonder if anybody has experienced a similar problem. I have a 2003 S40 Sport Lux and for sometime the main light on the driver's side seems to have a mind of its own. Sometimes its on and at other times its not. I've tried the obvious by trying a new bulb but to no avail. Any idea where to start looking for poor connections etc. Any help would be appreciated.

[caprirob]

Do a search for "CEM"

It will almost certainly be a dodgy relay in the control box under the drivers side underdash panel

Its fixable with a couple of cheap relays from RS Components if you can solder and you attend to it sooner rather than later - well known issue with these cars.

[mickaleen59]

You could try the wiring connector on the bulb (2 pin H7 or 3 pin H4) as these tend to get dodgy over a period of time as the LH one did on mine (2003) car.

You can find replacements with sufficient wiring attatched in Halfords / other motor factors and just cut off the old connector and what can usually be some of the wire gone hard from heat, hence dodgy contact.
This worked on my car anyway

[m1tch1987]

I take it its not a HID lol

[ciaranr]

It does sound like a connection issue from your symptoms, I had the CEM relay for left hand side headlight go, but the bulb went off and stayed off. 2V was constantly present at the bulb holder when headlights were on.

[cookie]

http://www.ebay.co.uk/sch/i.html?_tr...at=0&_from=R40

think you need to check the number on yours, and they need to match

[ciaranr]

Originally Posted by cookie

http://www.ebay.co.uk/sch/i.html?_tr...at=0&_from=R40

think you need to check the number on yours, and they need to match

Hang on a bit, if you decide it's a CEM issue, it's really, really worth trying to find someone (you or someone else) who is handy with a soldering iron, remove CEM (instructions with pictures on here somewhere) and replace the two headlamp relays (only one really needed (faulty one) but as they're so cheap, might as well do both!). Current part number, which I have successfully used on my 2003: http://uk.rs-online.com/web/p/non-la...elays/2172876/

Grand total €10 inc delivery to Ireland.

[caprirob]

The CEM part numbers dont necessarily need to match - they are interchangeable but you do need to check compatibility there are various threads on here which confirms what is compatible with what

One of the main considerations is if you fit an S40 CEM to a V40 you wont have any rear wiper control unless the CEM is reprogrammed first.

Likewise if you have foglamps and the new CEM came from a car without it may need programming to work.

I paid £35 or so from ebay for a CEM from a V40 with a different part number to the one that was on the car and it works fine - may have just been luck and the fact that I got the seller to check it was 100% working before he shipped it to me.

If it is the relays that are faulty new ones can be soldered in as per the comments above ( it is very fiddly though )

Where I came unstuck with mine is that the previous owner of the car when one relay failed rather than replacing it he simply bridged a wire from one headlight to the other across the engine bay so that one relay was powering both lights - which ultimately fried the CEM and knocked both the headlights out one night at 10pm on the M6 when I was about 50 miles from home - had to drive home on full beam with the headlamp adjusters wound down !

I then spent ages desoldering the old relays and then soldering new ones in and it still didnt work - the ultimate cure was a good used CEM

[DXMachina]

I wonder if the 'weak point' of the relays could be solved by using the relay feed from the CEM to power another beefier relay under the bonnet, which in turn would power the lights straight from the battery.

it strikes me that switching a 55 watt bulb at 14v indicates 4 amps, which is pushing the tolerances of a PCB-mounted plastic case relay (8 amps if some prior owner bridged the contacts as per above..)

A relay coil would pull a few hundred milliamps at most, thus reducing arc wear on the CEM relay contacts.

[ciaranr]

Originally Posted by DXMachina

I wonder if the 'weak point' of the relays could be solved by using the relay feed from the CEM to power another beefier relay under the bonnet...

Mine lasted 150,000 miles and 9 years, I really don't think it's worth bodging something up to potentially get a few more years out of it, while potentially causing another problem elsewhere!

CEM change to me is quite an extreme solution, if you have any chance of getting someone to have a go changing the relays first. I guess a good computer/mobile repair shop could do it.