Why don't some modern cars automatically turn off headlights when stopped?

Question

I forgot the lights on overnight on a 2016 Volkswagen Jetta and 16 hours later when I came back to the car the lights were still on but the car wouldn't start.

Can't the car check the battery level and automatically turn off lights if it had been stopped for a long while so as to prevent the battery from completely draining out?

As in, always keep a reserve charge enough to start the engine.

UPDATE two weeks later after reading all the answers: it makes sense to allow the user to leave the lights on even with they key out of ignition (e.g. setting camp, or locking the car while going to get help). But I can't think of any situation in which it would make sense for a car to let the lights consume so much battery power (presumably 8+ hours of continuous lighting) that the car will no longer start. Even if there were some such strange situation (watching snails drunk on molasses setting up camp during the arctic night), if lights go off automatically every, say, 6 hours without the key in ignition, I doubt any car owner would have a problem with turning them back on, but far more owners will be grateful they didn't have their morning plans ruined because they had to jump start the car after humanly forgetting to turn off the lights or not hearing the car beep for whatever reason.

Perhaps car makers have something to learn about battery management from smartphone makers.

Answer 1

All of these other answers go into weird philosophical directions...

The answer is much simpler than that:

Yes, it is possible to have the car turn off the headlights when the car turns off - many cars have an "Auto" setting for the headlights, and it does just this. They usually have a manual mode too, for those cases where you want the headlights on but the car is off.

Your car simply does not have this option. It was either an upgrade you did not purchase, or it's something VW decided not to offer on your car model. After all, the electronics to make automated lights costs money, and someone needs to pay for that.

Long story short, yes it's possible, just not with the factory options your particular car has installed.

Answer 2

This is another of those questions that can only be answered by a few people at VW, clearly the car could turn the headlights off after it is stopped; or after it is stopped and a certain amount of time has elapsed; or, as you suggest, by monitoring the battery and not allowing the battery to drain past the point where the car is likely to be able to start again.

The general answer to questions like this is that there are competing interests. For example:

• Making the car "idiot proof" and designing it to do what, as best the designer can tell, is the "right" thing in a particular situation. That would be easy in this case. Power to the headlights could be controlled by the load reduction relay and they would go off when the car is turned off.

• Deciding that most people are "not idiots" and letting them decide what how to use the car – for example allow turning on the headlights when the car is off as a source of light, perhaps while setting up camp or helping someone change a tire.

• Making the car "smart" and building a circuit that would try to balance the first two options. That's easily enough done, but it would add some cost and complexity to the car and there would also be an "opportunity cost" – why this feature rather than some other one. There might also be a philosophy question, especially if you have a strong assumption that people are "not idiots" – how is the car to know when it is better to keep the lights on and run the battery dead and when it is better to preserve starting power. Usually it will be the latter by not always, so now you have to add an override and teach users how to use it (or prompt them to make a decision).

The bottom line is that decisions like this are harder than you think and for a product that will sell 10s of thousands or maybe even millions of copies the choice that seems obvious to me or you may really just be the preference of an outlier. Further what's "right" in one market maybe completely "wrong" or even illegal in another.

Answer 3

Basically:

• sometimes, you need your headlights on even though the engine is off
• cars with "smart" systems like this are annoying if you i) don't know how to operate/disable the "smart" system or ii) the "smart" system is interfering with what YOU are trying to do.
• "smart" systems are expensive to engineer and need extra components/sensors, all this adds to the vehicle's sticker price. Cars are never designed to be "the best car ever," they are always designed with a price in mind.
• one more thing that can break. Imagine if the sensor for the "smart" system is incorrectly reading the battery's voltage (because of corroded battery terminals) and decides to disable some electrical systems for the battery's sake?

All this just in case you forget your lights on? There's a chime that will tell you your lights are on and the engine is off. This has saved me on a handful of occasions, but I do reckon that it isn't fool proof. Between the 2 people I live with, they left the lights on 5 times in the past year, leading to 2 batteries getting replaced, 2 jumps, and the last time I happened to be outside and noticed the lights on. I'd rather yell at them than have to pay for and deal with "smart" systems.

Answer 4

For what it's worth, my Subaru has what I think is the perfect solution -- headlights and parking lights turn off when you turn off the ignition switch. You can keep the headlights on all the time while you're driving and never worry that you'll forget to turn them off when you park.

If you really want the parking lights to stay on, there's a separate switch on top of the steering column for that (but in 10 years of owning the car, I've never needed it).

There's no way to keep the headlights on without having the ignition switch turned on, but I haven't found a use for that either.

Answer 5

It is about the complexity of the product. dlu has many good points like only the person that actually made the design decision may give the right answer. But it is probably not exactly about the opportunity cost. It is most likely a design policy of VW to not micro manage these cases.

• The feature has some connections with other features
• Change in a feature can effect the other features
• Adding complexity adds costs exponentially
• There is a higher risk of bugs
• There is also a risk of an illegal feature, the cars are audited for every market, so a simple design makes it faster
• Some safety critical applications have some coding requirement like that every line of code must be commented and such. Thus in a safety critical application these effect are even worse.

In your car you have things you really want to be fool-proof like brakes and steering. Any small feature that may make the car a bit more fool-proof but adds even a small change of messing with those critical things. tlhIngan introduced some errors that the system can do. What if those happened while driving, because some safety check was not implemented or if there was a bug somewhere else that led to the system think that the car is in safe. If the driving lights would be turned off in a non-lighted curve, it would be quite scary.

It is easy to see why VW might have a policy of not micro-managing features for some fairly rare scenarios, that do not introduce significant risk for the safety.

Answer 6

In many VAG cars, the lights stay on when you switch off the engine. Then a buzzer goes off when you open the door, to remind you to switch off the lights.

Since about 2008, with the addition of daytime running lights, the DRL are switched off automatically. The main/dipped headlights aren't though.

Answer 7

Actually, I just realized we're all overthinking it.

There's 2 types of battery power sources on all vehicles:

• always powered (think of your 4-way blinkers)
• "key on" power (think of your radio and clock, you need to turn the key to use them)

Some items, like the cigarette lighter and auxiliary power outlets, vary from manufacturer to manufacturer on whether they are always powered or only powered when the key is on. Case in point, I own 4 vehicles and 2 of them have the cigarette lighter always powered and 2 of them have it on "key on" power.

Other items are more consistent among manufacturers, like headlights and 4-way blinkers. These are both always powered because you could need them without having the key: 4-way blinkers in case you break down and need to leave your vehicle on the side of the road (you take your key with you), headlights/parking lights for a variety of reasons (maybe you're lost or broken down on an unlit rural highway in the middle of the night and need lots of light to look at a map/repair instructions/tools). This is a design decision that's been thought out.

So there you have it: if you want your headlights and parking lights to be off when the key is removed, rewire them to "key on" power like your radio. No sensors, no finicky smart systems.

Answer 8

I have owned/driven several makes of cars over the past 40 years.. my 2014 VW Tiguan is the ONLY one that requires manual turnoff of headlights the CAA rep who came to jump-start it laughed as he asked "First time VW owner?" PUT IN A SENSOR - feel free to remove the tire pressure. one that rarely works

Answer 9

My 2012 Volkswagen Golf has automatic headlights which are connected to a sensor on the windscreen and turn on automatically when needed. Removing the key from the ignition switches them to a mode where they switch off within sixty seconds.

The cars headlight switch also features the traditional positions of off, sidelights and dipped headlights. When in the off position, the car displays daytime running lights when it's ignition is on. If left in the sidelight or dipped headlight position, the car will continue to display sidelights with the key removed until the battery finally runs out.

As Microsoft are so fond of saying "This behaviour is by design." If you don't want your cars headlights to remain on for sixteen hours after being parked, place the headlight switch in the Off (or, if fitted, Auto) position.