Piston Slap: MKV GTI Daytime Lights: Running Out of Time?

by Sajeev Mehta

Published: August 18th, 2009

piston slap mkv gti daytime lights running out of time

TTAC commentator talkstoanimals writes:

The recent TTAC flap over the Priapus’, er, Prius’ potentially failing HIDs got me to wondering if turning of my MKV GTI’s daytime running lights would lead to any meaningful gains in HID bulb longetivity. Historically, I only tend to keep cars for approximately 80k miles. I also like the fact that DRLs mean I never forget to turn on my headlights in the rain—a requirement in many states in my neck of the woods. However, I like this GTI so much that, the car gods willing, I may keep it longer than my other cars.

So is it worth it to shut the DRLs down and possibly keep the bulbs in action for a longer period of time? Or would the potential gain be so small that it fails to offset the potential for forgetting to light the Xenon fires in the rain? (I never had a problem remembering to turn on the lights before my cars came equiped with DRLs, but I’m not getting any younger and neither are my memory banks.) Lastly, how does one turn off the DRLs in a MK V GTI? My owner’s manual sheds no light (groan) on the subject.

Sajeev answers:

Conspiracy theory alert! When the DRL issue came to “light” (double groan), I thought the battery lobby pushed hard to bring this supposed safety feature stateside. Which worked great in frozen Nordic countries, but has little to no statistical benefit to car accidents in the mostly-thawed US. And demanding more electricity on a regular basis has some amount extra wear and tear on the car’s charging system. Hence my paranoia.

Back to your HID + DRL dilemma. I cruised VW forums and the best way to kill DRLs without hacking wiring (usually not a good idea in a VW) is to buy a European headlight switch, and then reprogram the computer to accept said Euro-toggle device. FAIL: that’s pricier than a new pair of HID capsules, so . . . leave well enough alone.

Bonus! A Piston Slap Nugget of Wisdom:

I’m no Daniel Stern, so when in doubt, I ask Daniel Stern.

“You won’t realize any practical increase in HID bulb longevity by deactivating the DRLs. What is hardest on HID bulbs is turning them on, not leaving them on.

If you nevertheless wants to turn off the DRLs or alter any of the car’s other lighting parameters, it’s done with VAG-COM, the VW computer interface. A Google search focusing on the VW forums will give full info.

As for DRLs in the rain: Sure, but while most VWs turn all the exterior lights on full-time with the DRLs (or have an ambient-light sensor to turn the parkers, markers, and tails on when needed), lots of other DRL-equipped cars don’t, so it’s important not to put too much faith in the DRLs.

In most cases, you still have to turn the headlight switch all the way on when it’s dark or stormy to display low beams, sidemarkers, and taillamps for adequate visibility and safety.”

[Send your technical queries to mehta@ttac.com]

Sajeev Mehta

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2 of 64 comments

Toasty on Aug 19, 2009
ttacgreg: Personally I believe if some one is not mentally prescient enough to see an approaching vehicle in broad daylight, a set of head lights won’t matter. Since we're fairly sidetracked anyway... Many drivers may not be "prescient enough to see an approaching vehicle in broad daylight", but what about the wide variety of lighting conditions other than daylight and complete darkness? A major complaint of DRL opponents has been addressed by modulating light output to 30% or so while operating in DRL mode. This solution (or using the forementioned LED solution) seems to address concerns on both sides of the debate. There's a problem with relying solely on statistical analysis to discuss the efficacy of DRLs, or any other safety measure. There are instances where a smart DRL system has been effective, and to those people that avoided accidents, DRLs had a meaningful impact, regardless of the statistical significance. If a smart DRL system is designed to minimize glare, fuel economy impact, production costs, etc., I see it as a net benefit, even if it only has "a negligible effect" on accident rates. There are good DRL systems, so rather than condemn all DRLs, we should support the good ones.

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Gman37 on Aug 21, 2009

I had the same concerns as the OP for my MKV GTI so I used VAG-COM and use my fogs as DRLs. I could have disabled the DRLs entirely but I like the look of the fogs and they are cheap to replace (bought some Nokya yellows on ebay for 15 bucks).

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