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$1 Prius LED Brake Light Repair

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Mike Carambat, Jan 27, 2015.

  1. Mike Carambat

    Mike Carambat Junior Member

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    Ok, my 2005 Prius driver's side brake light went dim and needed a replacement. Apparently this is a common, but annoying and sometimes expensive problem as per some of the threads here. This is because the brake "lights" on this vehicle aren't replaceable as are the other lights, and is actually a 6-LED array sealed permanently into the light assembly. For most, the easiest answer is to replace the entire light housing which can cost $85-$350 depending on where you buy and if you do it yourself or not. However, it is possible to change the LEDs individually if one is so inclined, which is what this thread is about.

    Quite honestly, going the easy route and spending $85 for an entire new assembly and about 15 minutes of work to change it is worth the cost and I wouldn't recommend changing out the LEDs like this if you've got the time to order one and spend the money. But what if you've got somewhat fogged lenses? You might find a brand new and shiny assembly looks odd next to the other faded one and the cost of replacing two might make replacing a few LEDs look more attractive.

    So here's what I found out and did. Of course, I make no promises on how long this fix will last, make no guarantees on how well it will hold up to moisture, heat and weather, and if anyone chooses to do this on their own, you do so at your own risk.

    Step 1: I removed the assembly. There are only two nuts holding it in and one plug to disconnect. I got to them by partially removing the side panel. Instructions for removal are all over the internet.

    Step 2: I cut open the back of the top half of the assembly with a Dremel tool. See attached pics for where I cut. Once open I could easily see the back of the three LED light trays.

    Step 3: I unplugged the wires from the trays after recording their configuration. I then removed the screws holding the trays in place and slid them out.

    Step 4: Next, I located the bad LEDs. The replacement LEDs I used appeared to be about 3/4-4/5 as bright than the stock, so I didn't replace the entire set and kept as many bright stock ones as I could. I found the bad LED's by testing each LED with a 3v source (I used two D batteries taped together one behind the other and a wire attached to each end) An LED is a Light Emitting DIODE, so polarity is important and won't light if connected backwards. I found that the positive side is on the left when then tray is held with the connection tabs on the bottom with the LEDs facing up. Testing each one individually, I found the bad LEDs wouldn't light at all, or were very dim. I found three that had gone bad.

    Step 5: I pried out the bad LEDs with a small flathead screwdriver.

    Step 6: Using needle nose pliers I opened up a bit more workspace in the plastic surround where the LED used to be. I scuffed up the flat metal contacts with an exacto knife and applied a drop of solder on each of the two contact leads in the roughed area to help the solder get a good grip.

    Step 7: I then soldered in the new LED replacements. After doing some reverse engineering, I found the stock LED's to be 3.5volts each and pulling about 140mA each. That's a very powerful LED. The closest I could find at my local Radio Shack that fit in the housing was a 4-pin high brightness Red LED item # 276-0020, which were on clearance sale for just .17 cents!! And although only half the amperage as the stock, it's the closest thing I could buy locally without having to wait to order something else, and although just a bit dimmer than the stock, still works a treat. You can see the replacement LEDs in the pics below. The stock ones are round, the Radio Shack ones are square.

    Step 8. After repairing the trays, I reinserted and screwed them down and wired them back up.

    Step 9: I put back the plastic piece I previously cut away and sealed the back with silver ventilation tape (the thick metallic stuff used in AC duct work)

    Step 10: I then put the assembly back into the car.

    It took me about 2 hours of work. Like I said, replacing the entire assembly is way faster and easier, but for those looking for this information, I thought I'd post it.

    Also I drew a schematic of how the lights are wired together. Toyota designed a VERY clever mesh arrangement so that if one LED goes out, the others all still have a way to stay on, yet at no point do you ever have less than 3 LEDs in a series row. It's really a pretty amazing little circuit.

    Some additional information:

    The lights are fed via a resister pack in the base of the assembly. There are (4) 10 ohm resisters in series that feed the lights. I have no idea what the other set of resisters is for other than to provide a dummy load back to the brake light signal. The LEDs are setup in a mesh series arrangement so each light gets a third of the 9-10 volts coming out of the resister pack. The lights can take a bit more and less than that, so the difference in amperage of the LED's I suggest using seems to be negligible.

    That said however, I think I know what causes the failure in these LEDs.

    At one point I had both the driver's side and the passenger side assemblies removed for testing and I found that the 10 ohm resisters in the bad assembly were actually around 7 ohms even though they were supposedly rated at 10. That's a pretty significant difference and would result in a higher voltage being sent to the LEDs, thus overpowering them over time. I don't know if this was just poor quality control in selecting resisters or if they failed over time in high temperatures. I ended up leaving them as they were for now, as my measured voltage at each LED in the newly replaced boards were still under 3.6v each.

    Also, I found that the passenger side dummy load resisters value is HALF that of the driver's side. This makes me wonder if these resistors are used for discernment to tell the car's computer the status of each assembly. I really have no idea but would love to know for sure.

    Anyway, this was a fun little project, and for .17 each, I couldn't beat the price of the LEDs. I went ahead and ordered 12 more of them as my local Radio Shacks only had enough for the ones I needed to replace.


    IMG_6463.JPG
    IMG_6466.JPG IMG_6490.JPG IMG_6491.JPG IMG_6493.JPG IMG_6494.JPG IMG_6498.JPG IMG_6500.JPG IMG_6504.JPG IMG_6508.JPG
     
    #1 Mike Carambat, Jan 27, 2015
    Last edited: Jan 27, 2015
  2. bisco

    bisco cookie crumbler

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    wow, you are adventurous, well done!(y)
     
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  3. kingnba6

    kingnba6 Active Member

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    great writeup!
     
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  4. Mendel Leisk

    Mendel Leisk Senior Member

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    LED is becoming a dirty word for me, wonder if I'll rue that we have LED headlights. They're nice, but I've heard horror stories about replacement cost. :eek:
     
  5. JC91006

    JC91006 Senior Member

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    I don't know much about led bulbs but won't the other ones that you didn't replace soon fail?
     
  6. Mike Carambat

    Mike Carambat Junior Member

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    More than likely they will indeed :) But when they do I'll replace them with the ones I ordered from Radio Shack online. If I could have found more than 4 in local stores I probably would have done them all while I had it open, but also the stock ones are a bit brighter so I opted to leave em in there until they die.

    I've been following a thread going about converting the HID's to Halogens here:

    Converting HID Headlights to Halogen | PriusChat
     
    #6 Mike Carambat, Jan 27, 2015
    Last edited by a moderator: Jan 30, 2015
  7. R-P

    R-P Active Member

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    Thanks!!! I always wondered about the LED's but know (from experience) better than to open up working parts to satisfy my curiosity :ROFLMAO:

    The following story is long, too long for many and not meant as critizism toward Mike Carambat!!!!! He had nothing to loose and made a valiant effort to fix a lost cause and still managed to succeed!

    That being said, here's some questions, calculations, thoughts, etc.

    Judging by your pictures, the dummy load is four 43ohm resistors in series and the current limiting LED's are four 5.1ohm resistors in series. Is that correct?
    So roughly the dummy load is drawing 80 milliampere. (From your words, I gather this is the left one and the right one is half that resistorvalue and therefor double the current: even using a relay (e.g. 100mA draw for the coil) for a trailerhitch would already significantly mess with the total of only 300mA or so for a brake light, let alone simply hooking it up in parallel (like most people including me have done) but that's another story...)

    The LED's are in a clever arrangement as you say, which is basically two LED's in parallel, series wired with two more sets of parallel diodes.
    This does mean more LED's will keep burning when one fails (great they keep working when one goes for safety reasons!!!), but at the expense of the other ones failing faster too.

    I am puzzled by the fact you had multiple LED's fail. I would expect two to fail, being two that are wired in parallel: one fails, the other gets more current to handle and goes too. I did see something similar in a 7-LED-domelight in a car recently, but I cannot properly explain it.


    Some general information on LED's:

    As said, they are Light Emitting Diodes. They emit light when you run a specific current through them and only when going in the right direction (like other diodes, they block current in one direction and let it pass in the other direction). I say "specific" as this current is very important and should be between strict boundaries which are LED type and model specific.
    That's why it is very dangerous to attach a battery directly to an LED. It will either not light up or burn out.

    The reason it does not light is that an LED needs a minimal voltage to work, e.g. 1.8V for a typical 1990's red LED. If you use 1.5V, it will probably not even light up at all. If you use 2V, it will probably burn out already, that is how tight the limits are.

    So although the two D-cells in series worked a treat to find the flawed LED's, it is not common practice to find defective ones this way.

    In school I learned that an LED is ALWAYS to be used by a current limiting resistor. In the above example of the 1990's 1.8V LED, it will draw e.g. 10micro ampere (0.00001A) at 1.5V, but 2000 milliampere (2A) at 2 volts for a second (and then nothing because it burned out).

    The datasheet of said LED will give you information on what current the LED likes (e.g. 10milliampere) and what voltage it will drop at that current (1.8 volts).

    By using a resistor in series, you can limit the current the LED will be getting from e.g. a car (12V).

    We know you want 10milliamperes to run through the resistor and the LED. And we know the LED 'eats up' 1.8 volts, so the resistor needs to 'eat' (12V minus 1.8 volts=) 10.2 volts.

    There is a very simple and often used formula telling us that Voltage (V) is current (I) times resistor value (R), or V=IxR. Reworking this gives R=V/I. So the resistor value should be 10.2 volts divided by 10 milliamperes is 1020 ohm.
    There is a system behind what resistors are available, and we could find a 1020 ohm resistor in a good electronic component store that stores E96 range resistors, or we could get a 1000 ohm resistor in ANY store that caries resistors. 1000 ohm would do quite nicely.

    Just a thought experiment: what current will run through the LED when the car starts and produces 14.4V? The higher current might mean the LED now 'eats up' slightly more than 1.8V, but we'll disregard this minute difference. The (hypothetical) LED is rated for 10milliamperes typical current, 5milliamperes minimum current and 20milliamps maximum current, so will work fine when within these limits. Will it work in our example once the car is started?

    Answer in white: Resistor now needs to drop 14.4 minus 1.8 is 12.6 volts. We chose 1000 ohm, and reworking the formula gives I(current) = V/R or 12.6/1000 is 12.6 milliamperes. The LED will light brighter but still be well below its maximum currentrating of 20mA, so it is safe to use like this.


    You see here (assuming you got the same results as me) that the resistor "limits" the current through the LED. Even when the voltage fluctuates.

    Back to the Prius example: assuming the LED's 'eat' 3 volts a piece, there is still ~5 volts to be dissipated by the resistors (14.1 is the voltage often seen on my Prius, minus three times 3V (three LED's in series) = 5.1V).
    Assuming the four resistors are indeed 5.1ohm, gives us exactly 250mA of current going into the LED array (5.1V/(4x5.1ohm) = 1/4 = 0.25). Since there are two equal paths, each path gets half of this current, so the LED's get 125mA each (slightly off from the value Mike found).
    The reason I am doing this calculation is to warn that it is quite likely that the new LED's are going to die a lot faster, as they are being run at a far higher current than their typical currentrating.
    I couldn't find a maximum rating, so not sure it will last.

    It would be best to change all LED's and adjust the current limiting resistorbank accordingly, but I am not sure that would be legal...:cautious:

    The LED's are rated at 70mA typical, 2.6V typical and 3.3V max.
    Maybe I can gets get my point across when doing the calculation in reverse: with six Radio shack LED's in place, what voltage would the light work at with typical voltage and current:
    Each path has three 2.6V LED's in series, which is 7.8V. And both paths use 70mA. So the current limiting resistorbank (of four serieswired 5.1ohm resistors equals) 20.4ohm gets 2x70mA=140mA run through it.
    V=IxR = 140mA x 20.4ohm = 2.856 volts.
    7.8 volts is dropped by the LED's and 2.856 by the resistorbank when using typical values. This can only be achieved by supplying (7.8 + 2.856) = 10.656 volts.
    Any higher supply value will ram more current through the LED's. At 14.4V, each LED is already getting (worst case) 160mA (!!!)
     
  8. Mike Carambat

    Mike Carambat Junior Member

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    Thanks for all the calculations on this :) I actually had considered altering the resistor bank to provide the right amount of voltage, but wasn't considering current (amperage) at all, because my understanding of amperage (and please correct me if i'm wrong, i'm just an armchair electronics guy) is that amperage isn't necessarily 'foisted' upon a device, the device 'pulls' only what it needs. For example,using a 5v 2000mA iPod charger with an iPhone, the iPhone will only draw what it needs, around 500mA. Voltage however, is another story. You can overdrive a device by sending too high a voltage to it. But back to amperage...If you use (2) D cell batteries to drive an LED, it will drive it longer than if you use a 3v watch battery. Although the same voltage, the D cells have a much higher amperage capacity, and thus last longer than the very low watch battery. The LED will only 'pull' what it's rated at until the source is drained. Potential voltage/amperage confusion aside however, the fact these LEDs pull half the load the stock ones do, will INCREASE the voltage sent overall to the circuit because the load is less and they are using fixed resistors instead of a variable voltage regulator circuit, so yes, over time this will accelerate the degeneration of the LEDs. But dude, at .17 cents each, I wouldn't have a problem replacing them in what I would hope to be around every 3-4 years, wild-*ss guess :)
     
    #8 Mike Carambat, Jan 30, 2015
    Last edited: Jan 30, 2015
  9. R-P

    R-P Active Member

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    Totally true.

    Provided the voltage is low enough, then yes. But if the voltage gets slightly higher, the current will skyrocket.

    Here's a nice graph from this link:

    [​IMG]

    It shows particularly clearly what happens to both a resistor and an LED when you apply a voltage.

    The resistor: 1 volt, 10 milli amps. 2 volt, 20 milliamps, 3 volt, 30 milliamps, etc.

    The LED: 1 volt, no current, 2 volt, 20 milliamps, 3 volt, no current because it is blown.
     
  10. rafinara

    rafinara Junior Member

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    I dit the same LED echange. It does not look pretty at all. I am using now some epoxy glue to put everithing back. I hope I can still get the correct angle of the srews since the upper most one had to be cut out together with the case.
    Bottom line is that the blake LED's work now.
     
  11. JohnStef

    JohnStef Member

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    My 2004 has a dead brake light array so I need to make the same repair, and I am of the same mindset as the original poster, do this ONLY if you like a somewhat lengthy repair because you like expanding your knowledge - and you are Cheap! ( I am cheap)
    I pulled the light assy off the car in the normal way. I started opening up the gap between the outer clear lens and the black body. After a bit I could see that hatch side (vertical edge) would pull away from top to bottom and the top edge and bottom edge as well. All by wiggling with a 1/2" wide thin steel blade ( it is a worn tool so all of the edges are rounded, this is ideal to not create sharp pressure points when prying thin plastic apart. All went well for 3/4 of the perimeter. The outer edge would not give up to prying, so I got the heat gun out and applied heat to the black body. It worked. It took some finesse but I got the clear lens off. Now the assy comes apart for the LED repair.
     
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  12. Mendel Leisk

    Mendel Leisk Senior Member

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  13. ODIOUS

    ODIOUS Junior Member

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    I have this problem on my passenger's side tail lamp.
    I want to solder new LEDs in there but am not sure which LEDs are the best for the job.
    Can you anyone give a little guidance?

    The brighter the better of course but I only want to do this job once and not have to get back in there to replace LEDs. Better to put the best & brightest in there now.

    Thanks in advance!
     
  14. R-P

    R-P Active Member

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    If you do put in very bright LED's, do try to match the light output to the other side and the remaining ones (if any) in the housing you're replacing them in.

    Also, the best way of giving them a long life is to not run them near their maximum: 20mA LED's run at <10mA will pretty much live forever.
    I think the Prius LED's are run near their maximum and still last ages, but do fail once in a while. Since LED's are certainly better than 10+ years ago, should make this a once-in-a-lifetime job.

    But I realise I haven't actually given you a brand or type to buy...:D