My nav screen used to be able to auto-adjust brightness for day and night. Now it just stays in either "day" or "night" mode and I have to manually change the setting. Is that a sensor problem, fuse problem or something else?

Thanks,

 

Nav screen only or other functions as well?
Naturally, the nav screen can't update to day/night until it gets a valid GPS signal? AFAIK this works only on time and might be indeterminate for a while around dusk or daylight saving..Also, there are settings for day/night screens.
(it wasn't clear what you'd tried, apologies if this is sucking eggs)

 

I thought the screen brightness is connected to automatic headlamps (makes sense, no?) It used to be able to switch between day/night mode automatically. The automatic headlamps work fine. All other nav screen functions are normal. I don't mind having to switch day/night manually but would like to solve the mystery someday.

 

Do you have day running lights set in the menu? Not sure without checking again, but I noticed my LCD screen was dim in daytime, and I have day running lights on. Also, if in doubt about other headlights, set it Off for a check.

 

The Nav screen flipping between day/night mode has nothing to do with GPS signals. It is based entirely on whether the headlights are on or off.

I had this same symptom a couple years ago, and it turned out to be a couple broken wires in the turn signal stalk, which is a fairly common place for wires to break. Over time I started having a couple more flakey symptoms, which is what helped lead me to the turn signal stalk. It is an easy job to remove the stalk, and open the black box at the base of the stalk up to see if you have broken wires or not. There are two or four screws to remove on the underside of the steering column to remove the lower plastic steering column cover. Once the lower cover is off, the turn signal stalk simply unclips and slides out. The trickiest part of the job is popping the cover off the base of the turn signal stalk, which may require a second set of hands to help push in 6 or 8 tabs simultaneously. If you do find broken wires inside the stalk, your options are to replace the stalk (readily available for roughly $400-500US) or if you are handy with a soldering iron, you can solder them back together and protect them with some heat shrink. I repaired two broken wires in my stalk, and have had no issues since.

 

The light sensor is located on top of the dash in the centre of the windscreen but the fault is most likely
a broken wire in the stalk.
If you can't fix it used parts are on E bay Uk for not a lot of money.

 

Sorry, rhankey is right.
Today, taking a special interest, with the headlights on Auto the nav screen kept switching day <-> night as I went through late afternoon shadows.
Presumably the headlights were switching too, but I couldn't get out to check while I was driving.
With headlights or just sidelights on, the nav screen stays in night mode. Daytime running lights does not affect it.

Personally I'm not too keen on Auto-Headlights. With my other car as well (Honda) it's like lights flash on as you go under a bridge. Needs more hysteresis to be practical.

 

Now we're getting somewhere. My headlights are always on auto but the nav screen does not switch day < - > night with the headlights. Apparently the 'electrical link' between the headlights and nav screen is broken. Hopefully someone somewhere will have a cure.

 

I don't know the electrical wiring, but I HAVE observed the 2nd longer part of rhankey's post. Just occasionally the headlights would switch off for 1/2sec when the indicator self-centred. Nav screen was the least of my worries. Touch wood, I'm still in monitoring mode about that.

Indicator stalks were invented in 1000BC. Why is it suddenly a problem on this car?

 

Because there is too much inside too small a space ! The switch controls indicators, headlights, and the trip computer. Failure part or full of these switches is quite common, (I had to have a new one on my last X350). The switch is also used on the aluminium XK and the XF and may be used on other models). Cost for my switch was not outrageous at around £120, but what they cost nowadays I'm not sure.

 

The auto lamps function and the auto screen brightness function are two entirely separate functions.

Auto lamps (selected on light stalk) simply switches the headlamps on automatically if the ambient light levels fall below a certaing level.

Auto screen brightness mode is selected on the brightness/contrast adjustment screen, and if selected then it automatically changes all the screens (nav, climate, audio, phone) from day brightness to night brightness when the headlamps switch on. Auto screen brightness mode is selected by touching the 'button' on the RHS of the screen, marked 'Auto'.

If you press any of the three buttons on the LHS of the screen: Daylight, Night or Twilight, then it selects that screen brightness and that won't then change again until either you manually select a different screen brightness, or you select 'Auto' brightness mode again.

Twilight colours is a 'manual only' mode; ie Auto mode only switches between Day and Night.

 

I did some tests today to get to the bottom of the issue and found out my headlights and fog lights always stay on and cannot be turned off when the ignition is in the 2nd position or the engine is running. Cycling the headlight stalk to different settings ('Auto', 'off', fog light, etc.) does not change anything. Anyone got a possible fix?

 

You could try disconnecting the battery for half-an-hour or so, which is a form of hard reset for the various control modules. You'll need to remember to reset the window lifts afterwards, but that's trivial. I think the engine may run rough afterwards too, but that's only temporary while it re-adjusts the slow running settings.

 

It's almost certainly going to be a faulty turn signal switch as others have posted above.

 

That wouldn't explain the fog lights being on as well.

 

Ah, did not see the note about the fog lamps. That is correct, the fog lights have nothing to do with the turn signal switch. Fog lights are powered by relay R6, which is directly controlled by the FEM which reads the value of the fog lamp switch in the aux control panel.

Unless you want to fire the parts cannon and replace the FEM, I'd treat the fog lamps as a separate issue. Definitive diagnosis will be to run SDD and see what the commanded state of the headlight switch is in real time. Then diagnose the issue with the fog lamps.