Headlight low beam stopped working

[gotofms]

Hi,

I started the car this morning and everything was working fine. 

I stopped for fuel and for the first time ever I never switched off the lights and stopped the engine (don't know I didn't turn off lights as that's not usual for me). 

When I started the engine I had no headlights. 

The sidelights work, full beam works and the daytime running lights work. The dim beam doesn't. 

I changed the fuses to see if it was that, and still nothing. 

 

On the dash the light on the headlight switch/knob doesn't come on either. It does work for the sidelights which is on the same knob (and full beam on the dash works).

 

Does anyone know what could be the issue?

Edited 28 October, 2023 by gotofms

[Kostas123]

I don't believe the low beam light should light up on the switch, only the sidelight symbol lights up on mine. Does the interior switch backlights come on when you switch it on? Does the dash (with the gauges) lights up when you turn the switch from sidelights to low beams when it's dark outside?

[gotofms]

Hi,

Yes, all the interior lighting works fine, the dash lights up when I switch the light switch/knob to on, as does the light on the switch/knob (sidelights) to 'green'. 

Everything else is working apart from the actual low beam lights. 

Dash lighting on (as if I have low beam on), light switch light on, full beam works, sidelights work, rear lights work, reg plate lights work, front daytime running lights work and fog lamps and reverse light are all working fine. 

 

Just spoke to the wife and she said on Wednesday she had issues with the headlights (hasn't told me until now). 

 

[gotofms]

I've managed to fix the issue just by buying two new bulbs. 

 

I'm doubting both bulbs have blown at the same time?

[Kostas123]

26 minutes ago, gotofms said:

I've managed to fix the issue just by buying two new bulbs. 

 

I'm doubting both bulbs have blown at the same time?

Inspect the bulbs, is it actually blown?

 

Also I reviewed the wiring diagram, and there isn't much that can go wrong - lights and the switch connect to the "Onboard supply control unit". The switch gets power from fuse C14, but also from C31 (probably just the illumination of the switch). I believe the switch is fine, since the switch position is sent via a single wire, so if the gauges light up at night, then it's working. The control unit itself is a black box within the current flow diagrams, however it seems that the front lights go thru the C1 and C4 fuses. In that case I believe no lights at all would work, not only the low-beams. What's left is the wiring itself and connectors. Perhaps corrosion?

Edited 29 October, 2023 by Kostas123

[MarkWalsh]

I'll add a tidbit if your dipped headlights aren't working as they should, check that the alternator belt isn't loose - it's then not turning the pulley properly. You can observe this by dimming and brightening the headlights.

[MarkWalsh]

When checking for looseness of the alternator belt, also pay attention to its overall wear and tear

Edited 24 February by Gizmo

[J.R.]

2 hours ago, MarkWalsh said:

I'll add a tidbit if your dipped headlights aren't working as they should, check that the alternator belt isn't loose - it's then not turning the pulley properly. You can observe this by dimming and brightening the headlights.

 

That suggestion has been pretty much irrelevant for the last 30 years since serpentine poly V belts and automatic tensioners became mainstream.