2008 S204 C220Cdi Rear Hi Intensity Fog Lights - 1 or 2??

[Chrishazle]

Quick question as car is booked for MoT Friday. I very occasionally get a warning message when starting the car about rear offside fog light failed, so tested today and it works but only offside not nearside. Should I have both or only 1? Car failed its MoT last Jan on corroded rear brake lines, cost me loads and was her first ever fail, don't want another one!
TIA - even if the reply is RTFM as I haven't and can't (age and whatever!).

 

[Trickythemerc]

Spook bulb failure warnings can be caused by, old bulbs approaching end of life, cheap chinese bulbs, bad earth ETC. Your car will probably not have a N/S high intensity fog light fitted. Fit a good quality bulb in the O/S and drive on brother.

 

[190]

My 2009 W204 has only one rear fog light and my previous Mercedes was the same. It's a sensible policy on MB's part to lessen the confusion between fog lights and brake lights. Only one fog light on the off side is required for the MOT.

 

[st13phil]

As @190 says, they only have an off-side rear fog lamp.

If you’re getting spurious bulb failure warnings then it’s worth examining the light cluster as the W/S204 rear cluster has form for the earth burning out. There have been a couple of threads on here about it, so a search should turn up details.

 

[Chrishazle]

Thanks all, I'm aware of the earth problem on rear light clusters, but as everything else works OK I don't think it's that.

 

[DSM10000]

I had multiple bulb failure warnings on my W203 and W211 and each time the bulb was working.

Changing them for a new one solved it,

 

[190]

Spook bulb failure warnings can be caused by, old bulbs approaching end of life,

This is true. I've had a bulb warning when the bulb still functioned and a new bulb fixed it.

I presume that as the old bulb nears the end of t's life the filament thins and increases in resistance enough to trigger the bulb failure warning in advance of it actually failing.

 

[Trickythemerc]

That is pretty much how it works, plus the gas depletes. You can tell if a bulb is dodgy if the glass has started to darken due to gas loss.

 

[markjay]

Many years ago I had an ABS fault on the dash (Vauxhall Omega) that turned out to be due to a brake light bulb, which was working fine otherwise. This was looked at many times under warranty to no avail, until an older, more experienced tech proposed to replace the bulbs, and he was right.

 

[Chrishazle]

Thanks all, I have spare bulbs in the back of the car so will change the bulb before the MoT just in case (should have done it today as forecast for tomorrow is morning windy, then heavy rain all afternoon, not a day to be on the front driveway working on the car!!).