Daytime Running Lights (DRL) disable test results on 07 Matrix

Discussion in 'Fuel Economy' started by MPGee, Jul 19, 2015.

  1. MPGee

    MPGee Active Member

    Thought you all might want to know my test results from disabling the daytime running lights on my 2007 Toyota Matrix.

    Reasons I looked into this were:
    #1. I'm hungry for MPGees... of course.
    #2. Drivers might be confused by my headlights turning on and off, when I kill the engine at long stoplights and railroad crossings.
    #3. I work somewhere where they ask you to dim your lights when you pull up to the guard shack, so as to not blind them.
    #4. To prolong the life of my bulbs

    Unfortunately, the way Toyota designed this car, there is no way for the driver to turn off the DRLs, or stop the full light set from illuminating when the car decides it's too dark. I was hoping there'd be a fuse I could yank. No such luck. You have to snip a wire. I am about to go outside and try the method of snipping red/white wire #12. The video at provides a quick shot of where they are and how to do it.

    (I'm not looking to ignite a debate of safety vs efficiency here, as I've seen occur other threads... Do your own research and make your own choice.)

    Now for the quasi-pseudo scientific results:

    Testing scenario: out and back drive along the relatively flat highway here, maintain 60 MPH as best as possible. Weather: on/off showers, almost still winds. Rising morning temperatures. Kept electronics load as constant as possible, as this is essentially an alternator/electric load variable w/ the DRLs. I disabled the DRLs by disconnecting the headlight harness entirely (the same one shown in the video where you snip the wire).

    Run A: DRL on
    Run B: DRL off

    Run StartTime EndTime LowTemp HighTemp ElapsedTime AvgSpeed Gas(gallons) MPG
    A1 08:07 AM 08:49 AM 66 68 00:41:52 50 0.87 40.0
    B1 08:55 AM 09:38 AM 68 71 00:42:22 49 0.85 40.8
    A2 09:45 AM 10:27 AM 71 74 00:44:53 49 0.86 40.5

    The confounding factors are:
    #1. The temperature change, with it gradually rising
    #2. The heavier/more frequent showers on run A1. I had to do 10-15 windshield wiper executions, and the road was actually wet in a section or two. On B1 and A2 runs, there was only a slight shower, and the road was still pretty much dry.

    Comparing the average gas usage of A1&A2 to B1, this says that there's an improvement of 1.73%.

    But, since A1 was so much more wet, maybe we should discard that result. Comparing gas usage of B1 and A2 only, there's an improvement of 1.16%.

    But, since the temperature during run A2 was warmer than B1, the improvement is likely higher than that...

    My conclusion? Disabling the DRLs improves fuel economy by between 1.16% and 1.73% on a 2007 Toyota Matrix.

    I think my real-world improvement will be even better, as I've felt that the auto headlight sensor is overly cautious, turning on the lights when it's still plenty bright out...


  2. roothorick

    roothorick Active Member

    I would argue that's well below statistically significant. Tire wear, human element of how quickly you reach or maintain 60MPH, transient differences in wind, which will also affect engine temperature, hell, AIR temperature... these are all things that, in combination, probably give somewhere around a 3-4% difference in fuel economy, and they're largely uncontrollable. At this point statisticians brute force it and just get more data until their p-value whittles away to nothing. You're gonna have to drive a LOT with DRL on and off to get meaningful values, I'm afraid.

    Then again, I'm a filthy casual. I run whatever electrics I want whenever and I've got a subwoofer in the trunk that weighs quite a bit and draws enough current to demand a 6AWG power wire. So what do I know.
  3. MPGee

    MPGee Active Member


    I agree, that my results are nowhere near conclusive. I saw stats citing US Gov and Canadian (? I think) research both agreeing that DRL use decreases fuel economy. Where they disagree is by how much. One of them said it was an "insignificant" increase in fuel usage. The other said between 0.50-1.5%, if I recall correctly. Of course, I can't find said links right now. Closest I could find now is

    I haven't been able to find any sources that claim that they don't increase fuel consumption. Every page I search on this topic says that they do increase it.

    I also do agree w/ you that there are a ton of other factors that matter more, air temp, etc, that are out of a drivers' control. Traffic is a huge one.. But, as I want the best #s possible, I'm going do everything I can, within reasonable convenience, to slant the table in my favor.
  4. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    I have mine disabled. It must help with mpg in some small way, because it is a power drain. That doesn't come for free. How much, who really knows?

    My main reason is for my engine-off time - drl's drain the battery, so then you have to keep it running just to support the DRL's, wasting way more gas than the lights themselves consume.

    I have LED's for all my lights except headlights and turn signals. I upgraded the front marker lights so they're nearly DRL-bright. Most of the time I run with all the running lights on, which gives me rear lights as well for better safety.
  5. RedylC94

    RedylC94 Well-Known Member

    Without averaging a large number of runs as Roothorick mentioned, a simple theoretical approach might be just as accurate. Making rough guesses of 100W to power the lights, engine marginal BSFC of 305grams/kW-hr, and marginal alternator efficiency of 50% (??), I came up with about 61 grams/hr added consumption, which would be around 1.5% at your burn rate of about 1.5 gph. Surprisingly good agreement with your empirical results, huh? That percentage would go up considerably at lower speeds, of course.
    Last edited: Jul 20, 2015
  6. MPGee

    MPGee Active Member


    I've considered going LEDs for my lights. The thing that stopped me was the drastically higher prices, aside from the fact that you have to be wary of size, quality, etc. From what I can tell, they're all smaller companies making them, and just like CFLs, not all are as small as the bulb they are replacing. I recall reading about some people who bought them, then they wouldn't fit.

    What piqued my interest in disabling DRLs was that I recalled an interview or article about Wayne (I think) where it said that when he went for extreme MPGs, when driving he'd turn of all accessories, including radio and fan, so as to reduce current draw, and would wear a custom made ice-pack vest to stay cool. I was skeptical that DRLs or any electronics could have any impact on fuel usage, but I guess I was wrong... Although the increase in fuel consumption is small (and many would argue insignificant), it is enough for me to take notice. Biggest difference I've measured is most definitely A/C usage, recorded at


    That's some crazy math you got going there. I had to look up the term BSFC... I think I vaguely have an idea. lol. The Wikipedia page is pretty dense.

    If I'm going to get +1.5%, and I seemed to be averaging 37 MPG before, that'll be 37.555.... I'll take it!

    (Actually, that's kind of funny. I noticed while reviewing my AC thread that you both chimed in there. Hang around here much? :p I don't check here too much unless I have a specific point to research, or I have some interesting #s to post.)

    - MPGee
    Last edited: Jul 21, 2015
  7. PaleMelanesian

    PaleMelanesian Beat the System Staff Member has good ones. I've heard good things about V3 as well. Ebay - forget it. I tried several and they were poorly made / failed early / weak output / weird color.

    Yes, you pay a higher price. I'm willing to do that. Especially early on when you have a long time to pay it back. Overall I'm saving $30 of gas per tank. The lights are a small part of that, but will eventually be worth it.
  8. RedylC94

    RedylC94 Well-Known Member

    That math was pretty simple, I thought. My result is only as accurate as my assumptions, which I don't guarantee. That was just to demonstrate you can estimate the energy penalty of driving lights a lot easier than you could perform a sufficiently long series of physical test runs. It's more likely to be a fixed flow rate than a fixed percentage of mpg.

    BSFC (for brake specific fuel consumption) is a well-established standard engineering acronym, unlike some of the goofy home-made ones that get thrown around here. It's a measure of the efficiency of an engine, expressed as a ratio of fuel consumption mass flow rate to power produced under the same conditions.
  9. roothorick

    roothorick Active Member

    Well, A/C in most cars is *not* electronic. The AC compressor is mechanically driven by the engine, switched on and off via a clutch locking the compressor shaft onto a pulley on the serpentine belt. So yeah, expect significant MPG differences there.

    Only exceptions I know of are... all pure EVs of course, some Priuses (Gen-2 and Gen-3 I think).
  10. MPGee

    MPGee Active Member

    I agree Roothorick that AC isn't electrically driven. The thing that surprised me about whomever that was that made the ice pack vest was that they chose to turn off not just the AC, but also the fan. How much impact could just the ventilation fan make, at a low setting??

    And actually, regarding AC usage, I actually did some tests myself a while back. I found that on my car going 60MPH in a (more-or-less) steady-state, it came to about 10% difference. :)
  11. No Static At All

    No Static At All Active Member

    +1, not for such a miniscule difference in FE. I could only see disabling DRL's as being viable for those who EOC (which I don't do)

    Would NEVER get rid of my sub's or amp either. It makes driving so much more enjoyable.

    It's all about the bass!!
  12. seftonm

    seftonm Veteran Staff Member

    Does pulling the hand brake disable the DRLs? It does in most vehicles I've driven, I use that trick when in a situation like #3 above.
  13. No Static At All

    No Static At All Active Member

    Only if the brake is engaged before the car is started. Engaging the brake after the engine is running won't turn off DRL on the 1st gen Matrix.
  14. MPGee

    MPGee Active Member

    Really? Before I pulled the wire to disable DRL, on my 07 (last model year of 1st gen, if I'm not mistaken), if I pulled up the handbrake after the car was running & rolling, it would disable the DRLs. I had not thought of doing that at the guard shack, but then again, rolling up w/ my handbrake partially engaged seems like asking for trouble, in terms of forgetting that it's partially engaged.

    I've heard of guys driving around w/ their handbrakes engaged 1-click, but then again, strikes me as a bad idea...

    So far, I'm happy w/ my "mod" of killing the DRLs.
  15. roothorick

    roothorick Active Member

    Same on my Lumina. Must be a pretty standard thing.
  16. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    On the Fit the DRL is simply switched on and off by the parking brake. Brake off = lights on.

    That is, until I pulled Fuse #15 and disabled them. :p It uses the headlights on dim, so I can't just swap the bulb. I have brighter LED marker lights I use instead, with the bonus that my LED taillights are also lit for all-around visibility.

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