UK-POLOS.NET - THE VW Polo Forum

Hello all -

6N2 GTi has failed MOT because the O/S headlamp dipped beam light output is too low (the light output, NOT the aim). I'm not sure how these lights work or what could be wrong. The bulb "works", and replacing it and the ballast unit with spare ones doesn't fix it, tho' I can't be sure that the spares are 100%. I COULD try buying a brand new bulb but they are megabucks and non-returnable.

If it's not the bulb or the ballast, what could it be?

Help would be REALLY appreciated, as the car's now off the road because of this.

TIA....

Dave

Likely to be the bulb. When xenon bulbs wear out, they change in colour and can become dim, and change colour to red, green etc in some cases.

Have you tried the bulb on the N/S headlamp?

HIDS4U.co.uk sell the bulbs at a reasonable price

you should always replace these bulbs in pairs by the way - otherwise the colour will differ between lights

Many thanks for a really useful reply, Alex... swapping bulbs was going to be today's job. It's such a faff taking the back covers off the lights that I was trying to avoid working on both sides. There's a big risk of breaking the internal adjuster clips if I'm not very careful (and lucky) when I take out the bulb, so I was hoping to leave the one that works alone. Oh well....here goes!

D

I have a source for replacements if they break Just be delicate with them.

Hello Alex (and anyone else with ideas!).
Update:
1) Swapped bulbs: result - n/s is still bright, o/s is still white but dim. Conclusion: bulbs are both OK. So... is the ballast unit at fault? So....

2) Swapped ballasts: result - n/s is still bright, o/s is still dim. Conclusion: ballasts are both OK. Also tried 2 spare bulbs and ballasts - no change. Running out of ideas....

3) I KNOW... maybe there's a poor earth to the o/s unit? Check it - all OK.

4) I KNOW... maybe voltage to o/s unit is down? Check it.... both sides show 11.8v (this is BEFORE the ballast!).

Proper stumped now. The lenses are both a LITTLE cloudy but only a little, and both are about the same. The reflectors are both in good condition ( I've been right inside both units to fix the adjuster clips). There don't seem to be any deposits on the inside of the lens or "bullseye". The beam pattern is the same on both sides, so the bulb must be positioned OK; it's just the light intensity that's too low.

Help!

D

That's very strange

I assume you tried swapping the red igniter along with the ballast at the same time

It's unlikely to be a bad earth otherwise it wouldn't ignite

I think you may have an issue inside the headlight - you may need to take it off the car and have a look inside to check what's going on

Could be dodgy inside the projector. This is an odd one though.

Yes, Alex - I swapped the igniters as well; and I thought a poor earth would stop it firing up, but when you're clutching at straws it's worth trying.
Can't help thinking I must be missing something obvious, but what....! Opening the light unit means taking off the front bumper (again), and putting the lamp in the oven (again) to open it, etc etc. What a faff, especially as I'm pretty sure there's nothing wrong in there.

Watch this space. Grrrr.

Its very odd indeed

The earth comes from the loom, so youd be experiencing other problems if that was the case

Can you get a photo of the light output? Front of the car so I can see both lights on and against a wall.

Right, folks.... "and the answer is...."

It's quite logical. All my conclusions, and your suggestions, were correct. The electrics were all fine, but when I took the light unit apart. the back of the dip beam reflector had lost a fair bit of its silvering. I had bought a pair of 2nd hand lights from eBay - really for the spare bulbs/ballasts - and although the housings weren't usable, the reflectors were OK.

So I'm now the owner of a brand-new MOT. Many thanks for all help!

Point worth noting - I know these HID bulbs lose some of their output over time, but if you have a reduction in light output, new bulbs may not solve it. And it's very difficult to get into a light unit to see if the reflector has gone. Just a thought...

Glad to know youve fixed it