Piston Slap: The Underutilized Headlight Phenomenon

Sajeev Mehta
by Sajeev Mehta
piston slap the underutilized headlight phenomenon

TTAC commentator idesigner writes:


Last night during my drive home I saw something I see all too often: In the year is 2017, there are still cars and trucks that don’t have all their driving light on! Instead, they’ll only illuminate their front lights (and I can imagine dash light as well) but not tail or side lights.

What’s up with this? Aren’t auto manufacturers smart enough to fix this phenomenon? Why isn’t there a sound like the seat belt chime that tells you your lights are not on?

Sajeev answers

This reminds me of the time my mother received a warning from the police for not having her 1983 Continental Valentino‘s headlights on. Her valid-ish rationale was as follows:

  • Westheimer Road is well-lit, especially at dusk, and bright enough to not notice the lack of headlights.”
  • “The Valentino’s newfangled digital gauges are always illuminated!”
  • “The car-wash staff must’ve turned off the automatic headlight switch while cleaning inside, and I just assumed they were on!”

The late 1980s are not 2017, but the same phenomenon applies today as many new cars have:

  • Daytime running lights and/or purely ornamental LED eye-catchers incorporated into the front fascia.
  • Backlit gauges with multifunction screens that never turn off if the car is running.
  • A factory automatic headlight system either not ordered or owner-defeated.

So why can’t automakers fix this problem? Perhaps they will in 2018: headlight activation (with an integral low voltage cut-off like aftermarket stereo amplifiers) when the mandatory back-up camera senses darkness (or concentrated lighting from headlights behind) sounds pretty logical. In theory.

In reality, a dedicated ambient light sensor is likely necessary, which is another cost to pass down to the consumer’s wallet. Perhaps this is a problem with insufficient demand for a solution. What say you, Best and Brightest?

[Image: Shutterstock user norikko]

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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2 of 121 comments
  • V8fairy V8fairy on May 20, 2017

    Yes, so much - this is something that really irritates me too. People here driving in heavy rain or low light or both with no lights. So dangerous as they are so hard to see at a glance. I run my 2001 model daily driver with headlights on all the time, they turn off automatically as soon as I get out of the car once I have removed keys from ignition. My classic has a light buzzer that goes off if I open the drivers door with the lights still on - that from 1980. There is no reason cars produced today could not have lights on all the time, set to turn off when ignition off or similar, perfectly doable.

  • Andrew Andrew on May 27, 2017

    I know this topic is pretty much dead but I must throw in my two pennies. I drove shuttle for an Audi/Porsche dealer from 2007 to 2009 and their shuttle rig was a Q7 3.6 with the Premium package. It had the always-on electroluminescent gauges and AUTO lights and I kept them in that position but the morning driver always turned them to off, much to my consternation. One day I presumed they were on auto and entered a relatively long tunnel. About halfway through, the gauge pod slowly faded to off, summoning me to check the headlight switch. This is by far the best solution and can be incorporated with existing light sensors. It's so simple I don't know why nobody else has thought of it. Heck, I don't even know if Audi still uses it today.