Headlights-Low Beam

Isn't there somewhere a person can read this T-SB for free? Without signing up for whatever? It doesn't even come up on the Toyota.com website search. Did it apply to all 2011 models? I'm a little concerned since I drive a lot early in the morning, in the dark.

 

Sir: When it comes to light bulbs, I beg to differ: They're not just straight resistors. The filaments in standard tungsten bulbs have a massive positive temperature coefficient, meaning that the resistance goes 'way up when the filaments get hot. In fact, when one turns on a standard incandescent there's a current surge until the filament warms up. And that positive temperature coefficient isn't linear with temperature, either.

Standard Priuses use Halogen bulbs. I'm pretty sure the halogen refers to the gases inside the bulb; the filament is still probably tungsten.

There seems to be some evidence about that running a Halogen at reduced voltage does nothing good for the lifetime of the bulb.

What I do know: My son's 2002 Civic blew both headlamps. At about the same time. An ohmmeter revealed that they were dead open. So, he and I put in two more and the lights didn't go on then, either. Scratching my head, I broke out the shop manual for the car and started tracing wires. Turns out that the entire current for the lights goes through the light switch on the steering wheel; pulling out the switch, we discovered open contacts.

Naturally he was leaving the next day.. But, lo and behold, there was a Honda dealer parts department that was open late on Saturday. And they had the part! We hied over there, bought the thing, and that fixed stuff. (And a week later got a recall on the car for that specific part, they had been failing in droves.)

The interesting bit: High resistance in there was said to definitely lead to early light bulb failure and, yep, we saw that.

KBeck

 

Thanks for you info.. the dealer here was more than happy to repair the problem with the said S.B.--- no thanks bout had enough of this dealership.. just seems odd with o/e bulbs lasting so long and now after market fizzle in short order - we had "0" trouble with this car and it's like a switch was flipped it seems like it's falling apart over night. Several MAJOR repairs in a very short time frame-- rear hub bearings-- now head light issue-- an ABS signal issue (to which was back to dealer due to can't scan myself to pin point) but brakes go to default mode and dash lights up bad enough but seems to pick the most in - operatune moment like exiting on a rainy short exit ramp at rush hour. has anyone posted a video of the S.B. fix? I have the wiring coming bought said "harness" fix online for 1/4 what dealer was charging for 1?? also tossing about LED conversion kit which in theory solves 2 problems at 1 time.

 

Toyota doesn't like to talk about this serious engineering flaw. I suggest that you go to your Toyota service and request that theyrun off a copy of this T-SB for you. I gave my copy to service when I requested that they properly repair our car with no delay. They had no problem running off a complete copy for the mechanic. It is quite complete in instructions and takes a good bit of time to complete.

 

I will certainly grant you that; I learned something new today. Makes sense...

...but I'm still somewhat convinced that the current will go down if you put them in series, not up, which is really the argument I was trying to make. Maybe I should see if I have a string of incandescent holiday lights around somewhere that still works with one removed (and is also wired in series), and I can measure the current under both conditions.

In any case, you're also right about high/low voltages both causing stress; here's a useful note from Phillips on halogen bulbs:
http://www.lighting.philips.com/main/subsites/special_lighting/entertainment/Philips_Special_Lighting_2013/pages/chapter00/pdf/page_0092.pdf
The basics are this: The tungsten in the filament evaporates at a high temperature. At a moderate temperature, the halogen in a halogen lamp will react with tungsten as it evaporates off the filament. At low temperatures (like at the edge of the bulb), the tungsten-halogen combination won't do anything. At high temperatures, they'll separate again - and deposit the tungsten back on the filament, freeing the halogen to go catch another tungsten atom.

If you overvolt a halogen lamp, it evaporates tungsten faster, and the tungsten can remain free of the halogen further from the filament, because the temperature is higher and there's less free halogen to catch the tungsten. This can lead to tungsten depositing on the bulb, which darkens it, absorbs more light, makes it hotter, and can quickly escalate to a thermal runaway-type situation, ending when the glass melts, oxygen gets in, and the filament burns up.

If you undervolt a halogen lamp, then the temperature isn't high enough near the ends of the filament to break apart the halogen from the tungsten, and the overall rate of tungsten evaporation is lower, leaving more halogen free to react with the tungsten - including at these ends. So the halogen will carry the ends of the filament away to the middle, until all that's left is the middle, and the circuit is broken.

So the decreased lifespan is not due an increase in current from the positive temperature coefficient; it's a different balance in the chemical reaction inside the bulb.

Anyway, thanks for the chance to go teach myself something new.

 

I believe from my bad experience that Toyota realizing their wiring harness problem, instead of issuing a recall, provides a special low beam bulb with a standard industry number but with special design to work in their defective wiring harness. These bulbs last much longer than what you can buy at an auto parts house. Toyota supplies these special LB bulbs at a very high price. This is the way Toyota and other Auto manufacturers solve their design problems and at the same time make money on their failures. This Toyota supplied LB bulb is producing less light and that is why you can not see as well driving at night. The Toyota service people know this they just don't tell you. In most cases this is not their fault but they are directed by Toyota and their distributors to follow this directive.

 

It's a good hypothesis, maybe. But, just playing devil's advocate here, there might be a couple of holes to poke in it.

First, let's start off with lifetime a bit. Take a standard incandescent bulb, the kind that might (if it can be found) be put in a fixture in a house. A little thinking reveals that said light bulb lasts, in operation, a lot shorter than a car light bulb. There's a reason for that. At 120V and (say) 120W, this house light bulb would draw 1A and have a resistance (Volts/Amps) of 120 Ohms. Now, take a 120 W car bulb. That's 12V. To get to 120W, one would need 10 A. V/Amps again, and the filament would have to have a resistance, when on, of 1.2 Ohms. Hey - that's a lot less!

So, given that the radiative surfaces have to be about equal, this implies that the car light bulb has a much thicker filament that an house light bulb. (The bigger the diameter of the wire, the lower the resistance. Hair thin 30 AWG wire is a lot thinner, and higher resistance, than 12 AWG house wiring, no kidding. ). And, going along these lines, the primary failure mode of most filament bulbs that I'm aware of is the metal of the filament slowly evaporating (due to white-hot heat) over time. When too much has evaporated, then fzzt and the light bulb goes out. Hence, finally, a low-voltage bulb will then last longer than a high voltage bulb of the same wattage since said low voltage bulb has a thicker filament which takes longer to evaporate away.

There's a point to this, besides look-at-that. If one knows the voltage at which a lamp will be operating and there's a specification as to how many wattts the light will be dissipating, then there naturally falls into place the resistance of the filament and the gauge of the wire to achieve that, along with a lifetime that comes out of that.

So, this is where the Devil's advocate chimes in. Suppose we follow the argument that Toyota knew that they had a relatively high-resistance wiring harness and got a bulb vendor to build a bulb that could handle the reduced voltage. It's just as easy to put in a thinner filament and a lower wattage bulb as to put in a standard wattage bulb with a thicker-than-standard filament. There's probably limits on far one can go either way (if the resistance to the battery's too high, then one isn't going to get the wattage one wants, no matter what one does), but changing the filament to a thicker variety sounds like a better bet than a thinner, given that one would want the same power if possible.

The second Devil's advocate argument has to do with standards. I work and test stuff that is built to various types of standards, although I'll admit that light bulbs/LEDs don't get involved with I do too much. If one puts an industry standard part number on a part and says it meets standard-so-and-so, there's usually a standards setting organization (ANSI, anyone?) that has control by fiat going back to the US Department of Commerce (no kidding) and similar government organizations in other companies. When Radio Shack wanted to label coax with the RG-8A/U label but make it for cheaps with only 25% shield braid coverage, they had to go to the DoD and get it delisted as a standard, first, lest they get sued for false advertising. (Radio Shack still does stuff like that on CAT5E: I have a sample of their garbage on my desk.) In any case, I know for sure that things like hearing aid batteries that claim that they're a certain type had better do that under the force of law or face the consequences; I'm pretty sure based on this kind of experience that light bulbs made for cars follow similar standards.

So, maybe your post has something to it.. But there'd be some really peeved other light bulb manufacturers out there if they found out that one of their members was making an adulterated bulb, for cheaps, on the side.

KBeck

 

FAIR ENOUGH. Time will tell. THANK YOU

Please look under WIRING HARNESS. This T-SB is published there along with pictures, very professionally done.

 

This discussion has been somewhat....wait for it... illuminating.

Here's my tale of woe. In August, I was pulled over by Deputy Sheriff Doogie Howser in small town USA who had nothing better to do at 10:30 on a Friday night than bust my chops over my passenger side low beam which was out. He actually issued me a ticket with a fine, that would be expunged if I got the headlight replaced withing 24 hours. I went to my local Autozone and bought the "cheap" Sylvania H11, replaced it myself, took it to my local police department, where the officer signed off that indeed the bulb was replaced. I sent the summons back with the bulb replacement verification to the podunk town where I received the ticket. All good.

In early December, I was 200 miles from home with my wife on a weekend getaway, and I noticed the driver's side low beam was out. Crap. Stopped at a local AutoZone and they had a deal on the SilverStars. 52.99 and 10 dollar rebate. Replaced both bulbs (even the one I had replaced in August), so that I'd have uniform lighting on both sides. Outside in December. 20 degree weather. Ouch. All good. I actually liked the vision better with them with these, ummm aging eyes. Was pleased!

Just 2 weeks ago I noticed that BOTH low beams had burned out. Damn it. These bulbs lasted a little over a month. I called Sylvania customer service and to their credit, without making me produce a receipt or proof of purchase, they sent me two new replacement H11 Silver Stars via 2 day FedEx.

I haven't driven the Prius much since replacement, so as of now, the bulbs are functioning as they should. In August, this will become my son's car. I DO NOT want him to have these safety issues.

Will Toyota fix this wiring issue mentioned in the TSB at no cost? My guess is no.

And good on Sylvania for replacing their bulbs at no cost and with out question.

 

Yeah what gives? I purchased a used 2005 Prius in August and I have replaced the Headlights and rear running lights twice already!
My 1999 Jeep Cherokee XJ purchased in 2007 has never had any lights blow......

 

@sqwerty

Thanks for the info, I'll keep it in mind!
After mine blew 2nd I put the 35w 4300K digital HID kit and it hasn't been problem for 3 years now.