I would be grateful for any advice on a problem that has just recently developed with my 2006 L322 Vogue SE.
When the car is started in the dark with the headlight switch set to auto there is a delay of well over a minute before they turn on. Previously this was pretty much instant. I am wondering if there is a photocell somewhere that needs cleaning?

Interesting as I had the similar issue but never relied on the automatic position. I now tend to use them as & when. I believe the sensor is on the top of the windscreen & I have known issues on other vehicles where they don't work correctly.
How dark was it when you used them?, parked under a street light?.

I'll have a look at the manual, then have another look at mine & report back.

Update:- Thought that I would try the Auto route today & see what happens.
Well it appears that it works ok, If anything a little too sensitive. Dark area they come, as you would expect, however driving along the Motorway & B roads they were also illuminated.

Now the daylight was good & under these conditions I would normally Not have the lights on, there were other vehicles with lights on & many without.

I'm assuming that the sensors felt that it warranted the head lamp illumination, but how quick they switch on / off is difficult to tell.

I have added the details from the manual, But nothing more than we already know.
NOTE- This wording:- (Certain light and weather conditions are not detected accurately by the rain/light sensor. The driver should override the automatic headlamps function if in any doubt about weather conditions and the requirement for exterior lights to be active).

All the best,

AUTOMATIC HEADLAMPS
The automatic headlamp function is a driver assistance system. The driver can override the system operation by selection of side lamps or headlamps on if the ambient light conditions require front and rear lighting to be active.

The automatic headlamp system uses a rain/light sensor and the LCM, which are connected via the K bus and I bus to control the headlamp functionality.
The light sensor is incorporated in the rain/light sensor located on the inside of the windshield, below the rear view mirror.

The wiper system also uses the rain/light sensor for automatic wiper operation. Refer to the Wipers and Washers section for details of the rain/light sensor and automatic wiper operation. For additional information, refer to: Wipers and Washers (501-16 Wipers and Washers, Description and Operation).

The light sensor measures the ambient light around the vehicle in a vertical direction and also the angular light level from the front of the vehicle. The rain/light sensor uses vehicle speed signals, wiper switch position and the park position of the front wipers to control the system.

The rain/light sensor can detect if the vehicle has entered a tunnel or similar environment and will activate the headlamps on entry to the tunnel when the ambient and forward light levels have fallen quickly. When the tunnel is exited, the rain/light sensor detects the sudden increase in light levels and requests the lights to be switched off.

Certain light and weather conditions are not detected accurately by the rain/light sensor. The driver should override the automatic headlamps function if in any doubt about weather conditions and the requirement for exterior lights to be active.

The automatic headlamp operation uses ambient light levels which are monitored by a photo diode incorporated in the rain/light sensor. The rain/light sensor sends a lights on/off request to the LCM on the K bus, which responds by switching on the low beam headlamps, front side lamps and rear tail lamps.

The automatic headlamps are activated under the following conditions:
Twilight
Darkness
Rain
Snow
Tunnels
Underground or multi-level car parks.

Operation of the automatic headlamps requires the ignition switch to be in position II, the lighting control switch to be in the 'AUTO' position and a lights on request signal from the light sensor.

• NOTE: The front fog lamps will not operate if the automatic control lamps are switched on.
If the automatic headlamp function has been selected and the ambient light falls below a pre-defined level then the front and rear fog lamps can be manually activated. If the ambient light rises above that level then the fog lamps will be deactivated along with the rest of the lamps. If the ambient light then falls below this level again the lamps will be activated, but the fog lamps which were previously selected will not.

Worth baring in mind, they seem to know when the light from behind is brighter than the light in front (thanks to the sensors in the windscreen, and the ones in the rear view mirror that trigger the Electro-chromic dimming), and will come on to help make you more visible on the road during those "low sun" times.

Thank you for the replies.
I would abandon the auto lights other than my wife has become habituated to them and regularly leaves the car with the lights on in manual mode. I am forever going down in the middle of the night to switch them off.

Knowing now where the light sensor is I can see that it is clean and unobstructed.

In response to highroller the matter is a problem when starting at night. The sequence is as follows:
1. Start the engine with the lights in auto- position in the dark.
2. Lights revert to the last known condition - meaning if you last switched off the car with lights on in auto at night the lights will come on, else they will remain off.
3. If the lights did come on as above they will go off after a few seconds despite it being dark.
4. If you do nothing they will then come on and stay on after a minute and a half.

So my system seems to respond but with a long delay and a weird kind of memory issue.
My wife also reports that the auto wipers are also not as responsive. Do you think it is the entire light/rain sensor that is at fault or its connection to the LCM. Anyone know how I can troubleshoot the sensors vs the onward wiring?

Definitely sounds like a sensor issue, especially as you are experiencing wiper issues aswell. Try covering the sensor when the lights are on auto during daylight & see how long it takes for them to illuminate.
Unsure if the sensor can be reset if there is a problem.

All the best.

Thanks Highroller
I will try that out. From what you have said above it sounds like they should come on very soon if the sensor is covered.

So here is an interesting one. Cover the sensors during daylight and it takes about a minute for the headlights to come on, but uncover them and they go off immediately.

The lights & wipers work from the same sensor (above the rear view mirror)

I would start with the basics, a simple battery reset may well reset the rain sensor & the LCM...