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Discussion Starter #1
2014 Fiesta SE. I live in an snow belt area where cars are prone to rust and corrosion problems.

While driving at night with the headlamp switch set to AUTO, the headlights went out. I live out in the country so it was black. When I turned the headlamp switch back a notch to ON (wiring diagram calls it LOW), the lights went on. The autolamp function is, however, neither always ON nor always OFF. It is intermittent, but not with the meaning that it might not be dark enough. No, it's black outside, there's no stray light in the car that might be hitting the sensor, but sometimes the headlights are on, and sometimes they're off. I can't quite test it since it would mean driving around at night with the lights going on and off, but I suspect that if I were to leave the switch on AUTO, the lights would turn on and off and on again as I drove along. It doesn't sound like a sensor problem to me. Maybe more like an intermittent ground, but other features in the car seem reliable. The book suggests that problems with the headlamp switch would show up as a DTC, however, no codes are set.

My guess would be that the engineers made it that lights-on would be the failsafe position for autolamp, that is, if the sensor wires were corroded, the lights might turn on in the day, rather than turn off at night.

I don't want to blame the BCM, at least not yet.
 

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If I were you, I'd try unplugging the sensor. The auto function should default to always on (just a guess, maybe it will throw a code too). Then you could drive around and see if the problem occurs. If it does, then it's something with the switch. If it doesn't, then it's something with the sensor, it's connection, grounding or reading circuit (BCM?). Just my two cents, unless someone has a better idea.
 

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Yes, Raphael, that makes sense. I disconnected the sensor, and the lights do stay on. I'll drive it like that for a while, but not at night, and see if the headlights stay on. I should know by the little headlamp light on the dashboard. Thanks for the idea.
 

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Discussion Starter #4 (Edited)
Nope, not the sensor. The lights still go off even with the sensor removed. Also I noticed that the brightness of the dashboard lights sometimes flickers. I'll bet it's related. I'll keep plugging away at the problem and posting the progress, and, with some luck, the solution.
 
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