Brake Lights Not Working/04 Prius

If I recall there is a common ground wire. Also could be the brake switch (at the peddle). There have been other postings of the same problem. I wouldn't jump at replacing any lights or assemblies yet unless you see condensation inside the assembly. Could also just be one light messing the whole thing up. Pull one and see if it makes the other work.

 

Here is a recent post on brake light checking in case you haven't noticed it. Good luck!

http://priuschat.com/forums/gen-ii-...y-ecu-control-led-assembly-2.html#post1186027

 

There was a recall for the 04 brake switch. Attached is a copy of the recall.

 

Good decision and good luck!

 

Congrats on the restoration and one question: does the aftermarket part also use LEDs? Thanks!

 

I am having the same problem with my right side or passenger side brake light not working. I ordered the after market replacement assembly. Can you send me the link that shows how to remove and install the rear tail light assembly?

Thank U Very Much,

Frank
[email protected]

 

Jim, How is your replacement tail light holding up? Our light is dead and needs to be replaced.

 

I have not removed the rear lights from my car to check, but can the lights be dismantled in the same manor as the fronts (heated in an oven) and then replace any burnt out LEDS. Must be some way to implement a cheaper repair.

 

My right brake light failed last week. (It's six LEDs that are inaccessible until you destroy the light assembly by sawing it open.) I have a voltmeter and plenty of time, so I tested everything. The wires to the brake light first go to an electronics panel in the bottom of the assembly. (This panel is accessible, with a little coaxing.) This panel consists entirely of one diode (a current-direction control) and two groups of in-series resistors. The resistors are stamped with their ohm ratings, and you can easily see how everything connects on the printed circuit. All the resistors measured okay, as did the diode. The output voltage of this electronics panel measured about the same as the 12-volt input voltage. (I tested both the failed assembly and the good one, and got the same readings.) The LED bulbs in the bad light glowed when voltage was applied, but only at about 10% of their required brightness. I concluded that the LED bulbs must have blown, and that I had to buy a replacement light assembly. (The spouse sagely vetoed my economical idea of instead converting the white backup lights to red brake lights by changing the bulb color and repositioning one wire.)

Removing the tail-light assembly from the car requires maybe five minutes of removing interior panels to gain access (held in place by three bolts and numerous clips), followed by one minute to unscrew two 10mm bolts that attach the light assembly to the quarter panel. Reassembly requires one minute to mount the light assembly, followed by maybe twenty minutes to work the interior panels back into position.

Replacing the entire assembly fixed the problem, of course. I then sawed open the old light assembly with a saber saw, to look at the LEDs. I didn't cut enough to be able to see whether they are wired in parallel or in series. I pulled out one LED and applied 14 volts to it, and got the same 5% glow.

With labor charges so high relative to parts prices, I can't really blame Toyota for designing the LEDs so we can't fix them ourselves -- very few people would do that even if the LEDs were accessible and the parts were made available. But I do miss the days when the entire job of fixing a tail light or brake light or turn signal or backup light consisted only of popping out the old bulb and popping in the new one.

As to why the six LEDs burned out, and whether better engineering would have safeguarded them better, I can't even guess. I've read that LEDs are easily damaged by excessive voltage, and that resistors in series are therefore used to prevent a voltage surge.

I can post clear photos of one of the LEDs and of the electronics board if anyone asks me to.

 

Please post your photos.

- What was the value of the resistors on the circuit board?

- How many wires led from the board to the LED matrix?

- If all six LEDs failed at one time, I would assume that they had been wired in series...

- Did you apply 14V to one LED, without a current-limiting resistor in series with the LED? If so, I am surprised that the LED didn't burn out and open up (i.e., resulting in infinite resistance across the LED terminals.)

 

Patrick, good questions!

The resistors are 6.2 ohm and 24 ohm. (Five 24-ohm resistors, R-51 through R-55. Four 6.2 ohm resistors, R-3 through R-6.)

Two wires run from the board (CN2) to the LED array. Yellow wire is +, and black wire is -. The power to the board (CN1) is also two wires: Green wire is +, and black/white stripe wire is -.

I too assume the six LEDs are wired in series. Doesn't this necessarily mean that if one LED blows, none will illuminate?

Yes, I applied voltage to one LED, without a resister to limit the resulting current. I expected that 14v would burn out a functioning LED, so I started with 1.5v, then 3v, then 6v. The LED did not illuminate at all at those voltages, so I figured I could do no additional harm by applying 14v -- though I didn't expect to learn anything from doing so, since by then I figured the LED was already blown.

Before applying any voltage, I measured the resistance across the two terminals of the one LED light, and it was infinite.

Any opinions on the cause of the LED failure?

I'll post nine photos separately.

 

Nine high-resolution photos are now posted online. Click on an image to enlarge it. Click on the image a second time to enlarge it even more.

I'm too junior to be able to post a clickable link to the site where I posted the nine photos. They are at:

tinyurl.com/2dzubb2

 

I have also taken apart one of these assemblies. The design is poor, and not up to Toyota standards. There are two strings of 3 diodes in series. In addition, each diode is cross connected to the other in the string, so in effect, there are 3 sets in series of two diodes each in parrallel.
So, if one diode fails, the current in the string is now only going through 1 diode and not two. This gives the remaining diode a very short life, since it is running at 2x the current.

 

Thanks for providing the photos and commentary. Based upon those, I assume that the circuit consists of 120 ohms (5 x 24 ohm resistors) across CN1, plus the polarity protection diode D1 in series with 24.8 ohms (4 x 6.2 ohm resistors), leading to CN2 which allows connection to the two strings of three LED lights (per vertex). Do you agree?

I am wondering what is the purpose of the 120 ohm load across CN1? Since there are two rear brake light assemblies in parallel, this results in a net 60 ohm load, for a current draw of ~230 mA. Perhaps this load is intended to dampen voltage spikes that might appear across CN1?

Now let's consider the 24.8 ohms in series with the LEDs. Assume 0.7V drop across the polarity protection diode plus 1.8V for each red LED, the nominal 13.8V available would become 7.7V (since vertex says the LEDs are wired as two strings of three LEDs each).

7.7V / 24.8 ohms = 310 mA current flow available to power the six LEDs. Since there are two strings, then 155 mA might flow through each string. Hmm, this seems like a much greater current flow than I would have expected. vertex, are you sure that the LEDs are connected as two strings of three each?

If the six LEDs were in fact connected in series, then you would have 11.5V of voltage drop across the LEDs and polarity protection diode, leaving 2.3V. 2.3V / 24.8 ohms = 93 mA which still seems high.

 

They are clearly not standard 20ma LEDs, they look like the Lumileds SuperFlux units which IIRC are rated to 70ma each. That should put the total draw per side at 140ma. These kind of LEDs typically are over 2v forward, so this would affect your calculation. Until we have a datasheet, we will not know the forward voltage unless someone can check.

Assuming 2.5v, that puts the total forward at 7.5v which seems like a good number to still safely use resistors as the current source. All 6 of them in series would be 15v which obviously cant work, so that rules out that configuration. Going any lower would mean much larger resistors as there would be much more power loss. (say assuming 3 parallel strings of 2, or worse; 6 in parallel)

It's also very strange they bothered to use LEDs, but didn't just add some more resistors and another diode to also use them as tail lights. Many cars with LEDs use a more complex (and reliable) current source, such as a PWM controlled boost converter. The resistor-based circuit is not very reliable as any spikes can get through. There isn't any kind of regulation. I'm very surprised they didn't at least include a clamping diode of some sort to catch the spikes. Even the little LED in the glovebox has a zener!