I went to a shopping mall and when I came out, after about 90 min, my headlights were still on. The auto-shutoff didn't work. No harm done - that is not long enought to drain the battery - but if I had trusted the auto-shutoff when parking for the night, it might well have left a dead battery.

Why?

Turns out - the light switch on the driver's door. The SECU apparently expects to see:
- ignition off and key out
- driver's door open (light switch closes)
- driver's door close (light switch open again)
before it starts the timer to turn off the headlights automatically.

In my case the switch wasn't closing - the interior lights did not come on - so the headlights did not go off.

Took the switch apart, cleaned the contacts and lubricated with silicone grease, and all seems well now. If there are any future problems I will replace the switch.

 

When you say interior lights, is that only the dome? Or door lights as well?And can you show a pics of this switch please?

 

i wonder about that all the time when i get out of my car at places. that would suck if it were overnight.

 

I am talking about the switch on the B-pillar underneath the door catch. Sorry, I don't have a pic available, but it is not hard to find if you have the door open. The lights (dome light and door panel lights) are actually controlled by the SECU (Smart Entrance Control Unit, i.e. body computer) but the switch is the input to the SECU. The switch plunger is sealed inside a rubber boot and is activated when you open the door.

The point is, if you leave the headlight switch at the "auto" position and the door switch fails, the headlights will not shut off on a delay timer, as they are supposed to do. I thought that the battery possibly running down because the interior lights did *not* come on was a little amusing - usually it's the other way around.

Actually, after reading the manual, I discovered that either front door opening and closing will start the delay timer, but I didn't have a passenger when this happened.

 

thanks for the heads-up