# "CAN Bus bulbs should not be used in non CAN Bus applications"?



## protivakid

Hi, I see on the superbrightleds site that they say CAN bus bulbs should not be used in vehicles without a CAN bus, my question is why? From reading it seems that CAN bus LED's just use a resistor to draw the same amount of power as a conventional bulb which yes, is more than a regular LED, but in a car that was previously using the regular bulb anyway how can this hurt? Thanks!


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## bshanahan14rulz

LED bulbs do not provide the same beam characteristics as the bulb that the lamp was designed for. This is why LED bulbs are not recommended.


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## Steve K

what's a CAN bus LED? I'm familiar with the J1939 CAN bus, but it's a data bus and has nothing to do with LEDs. I can only guess that it's a light assembly using LEDs that has its operation controlled via the CAN bus?


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## protivakid

Steve K said:


> what's a CAN bus LED? I'm familiar with the J1939 CAN bus, but it's a data bus and has nothing to do with LEDs. I can only guess that it's a light assembly using LEDs that has its operation controlled via the CAN bus?



Below is an example of a "CAN BUS" led bulb from the site I mentioned before with the disclaimer not to sue them in a non-can bus application:

http://www.superbrightleds.com/more...78-led-can-bus-bulb--1-led-festoon/1264/2937/

And here is a link to a normal led from the same site

http://www.superbrightleds.com/moreinfo/festoon-series-bulbs/578-led-bulb-9-led-festoon/237/


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## Steve K

I'm not sure that those links explain what a CAN bus LED is, though. My initial assumption was that people were trying to power a LED from the CAN bus, but after a little poking around on the web, I'm starting to think that newer cars monitor the status of some of the car's lights (probably just detecting if the bulb is drawing too little current). Presumably, replacing an incandescent bulb with a LED causes the car's diagnostics to interpret the LED as a burned out incandescent?? That might explain the enignmatic phrase "error free LED" on some of the vendors' web sites.

It is a little concerning that the LED lights seem to be burning up extra power in order to not be mistaken for a burned out incandescent.. to quote one of the links:
"Error free LED bulbs are specifically designed with built-in load resistors to allow them to be used with CAN(Controller Area Network) Bus equipped vehicles without triggering the OBC (on-board computer), commonly found in European vehicles such as BMW, Audi, Mercedes, Volkswagen, Porsches"

It would seem to negate the efficiency advantage of LEDs, and just increase heat in the light fixture and cause an early death of the LED. 

Or am I misunderstanding the whole concept?

edit: to get to the original question: what's wrong with using a CAN bus LED in a non-CAN car? ... good question. I'll just assume that the CAN bus lights are designed to get cleaner power, and can be damaged (and fail in an unpleasant manner) if used in a non-CAN car. For all of their flaws, incandescents do fail quite benignly usually. Electronics, such as what is pictured in that CAN bus LED, subjected to large voltage spikes can fail in a violent and exothermic manner... i.e. it may go up in flames. It's fun to watch on the lab bench, but not so cool in your car as you drive down the interstate.


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## protivakid

Steve K said:


> I'm not sure that those links explain what a CAN bus LED is, though. My initial assumption was that people were trying to power a LED from the CAN bus, but after a little poking around on the web, I'm starting to think that newer cars monitor the status of some of the car's lights (probably just detecting if the bulb is drawing too little current). Presumably, replacing an incandescent bulb with a LED causes the car's diagnostics to interpret the LED as a burned out incandescent?? That might explain the enignmatic phrase "error free LED" on some of the vendors' web sites.
> 
> It is a little concerning that the LED lights seem to be burning up extra power in order to not be mistaken for a burned out incandescent.. to quote one of the links:
> "Error free LED bulbs are specifically designed with built-in load resistors to allow them to be used with CAN(Controller Area Network) Bus equipped vehicles without triggering the OBC (on-board computer), commonly found in European vehicles such as BMW, Audi, Mercedes, Volkswagen, Porsches"
> 
> It would seem to negate the efficiency advantage of LEDs, and just increase heat in the light fixture and cause an early death of the LED.
> 
> Or am I misunderstanding the whole concept?
> 
> edit: to get to the original question: what's wrong with using a CAN bus LED in a non-CAN car? ... good question. I'll just assume that the CAN bus lights are designed to get cleaner power, and can be damaged (and fail in an unpleasant manner) if used in a non-CAN car. For all of their flaws, incandescents do fail quite benignly usually. Electronics, such as what is pictured in that CAN bus LED, subjected to large voltage spikes can fail in a violent and exothermic manner... i.e. it may go up in flames. It's fun to watch on the lab bench, but not so cool in your car as you drive down the interstate.



Thanks for the input and time spend researching. You are correct that they basically draw the same amount of power as a regular bulb just so they don't trip the car's computer. Not a great solution but I guess it does solve the issue...

I still wonder why this site would warn you NOT to use them on a non CAN-Bus car though, it doesn't seem like they have any higher risk of "going up in flames" in a non can-but car as they do in a can-bus vehicle.


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## N8N

sorry, late to this thread... yes my understanding is that CAN bus bulbs are to be used in cars, usually German ones, that monitor every damn thing for failure (which is nice, so long as you don't deviate from factory spec) usually by using a resistor to increase current draw. I'd consider them inferior to ones without the resistor as we all know extra heat = bad and they're probably more expensive than the similar product without the load resistor.

I guess the other thing to keep in mind is that if the car is monitoring the bulb for failure it is probably a bulb that is part of a required, regulated lighting function therefore you might want to think about whether you really want to use a LED in that application or not. (don't know if that is true for all cars, but it seems to be on my BMW - e.g. I replaced the map lights with plain old LEDs on a board and they don't throw any errors, but I believe that every single exterior light is monitored for failure.)

I can think of reasons why you may want to do something like this that wouldn't necessarily be illegal, e.g. replacing a BMW's license plate light assemblies or taillights with ones from a later model car that use LEDs (very common) in which case you would need to either disable the bulb checks through coding or else update the FRM and code it in to make the car think it's a later model car. But things like replacing the angel eyes with LED "bulbs" should be approached with caution, as the angels are also your parking lights and DRLs...


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## protivakid

N8N said:


> sorry, late to this thread... yes my understanding is that CAN bus bulbs are to be used in cars, usually German ones, that monitor every damn thing for failure (which is nice, so long as you don't deviate from factory spec) usually by using a resistor to increase current draw. I'd consider them inferior to ones without the resistor as we all know extra heat = bad and they're probably more expensive than the similar product without the load resistor.
> 
> I guess the other thing to keep in mind is that if the car is monitoring the bulb for failure it is probably a bulb that is part of a required, regulated lighting function therefore you might want to think about whether you really want to use a LED in that application or not. (don't know if that is true for all cars, but it seems to be on my BMW - e.g. I replaced the map lights with plain old LEDs on a board and they don't throw any errors, but I believe that every single exterior light is monitored for failure.)
> 
> I can think of reasons why you may want to do something like this that wouldn't necessarily be illegal, e.g. replacing a BMW's license plate light assemblies or taillights with ones from a later model car that use LEDs (very common) in which case you would need to either disable the bulb checks through coding or else update the FRM and code it in to make the car think it's a later model car. But things like replacing the angel eyes with LED "bulbs" should be approached with caution, as the angels are also your parking lights and DRLs...



What I wanted to do was use a CAN-bus led as the dome light in a 2005 Dodge that does NOT have a can-bus. The reason being that the built in resistor actually helps to turn off the bulb completely where as by default the car delivers a very tiny amount of constant current to the dome light and when using a normal led the light will never fully shut off and stays very dimly lit. The fix for this by other users was to solder on your own resistor but if I were to use a can-bus led that has the build in resistor it would be as simple as popping in the new bulb. I just didn't know if there was any harm in using the can-bus bulb as a dome light in my non can-bus car.


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## Steve K

Interesting problem.... I'd certainly be inclined to just add a bit of shunt resistance to handle the leakage current that is causing the LED to glow dimly. Certainly there is an appeal to just buying a LED light that has that function built into it. 

Not that it helps you much, but there probably is a relatively small risk of the CAN bus LED failing in a "bad" way and setting your car on fire. The photos in the links you provided clearly show some circuitry that looks like a switching power supply, which could have worse failure modes that the simple LEDs on the non-CAN bus LED modules. 

You might try using the CAN bus LED for a dome light, but leave the cover off, and keep an oven mitt handy in case you need to yank a burning LED out of the light fixture while driving. Try it this way for a few weeks (with the dome light switched on), and if it doesn't burst into flames by then, it probably won't. 

A quick tip: some of the worst voltage transients on a car occur when you turn off a large electrical load. This might be the headlights or perhaps that 600 watt sound system. Put the car in park, run the engine at high rpm, turn the dome light on, and then switch the headlights on and off a number of times. (and keep the oven mitt on one hand, just in case) If that doesn't kill the CAN bus LED, it should be a very low risk.


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## inetdog

protivakid said:


> Hi, I see on the superbrightleds site that they say CAN bus bulbs should not be used in vehicles without a CAN bus, my question is why? From reading it seems that CAN bus LED's just use a resistor to draw the same amount of power as a conventional bulb which yes, is more than a regular LED, but in a car that was previously using the regular bulb anyway how can this hurt? Thanks!


To restate and summarize what has been said so far: 

1. The presence or absence of CAN bus electronics in the car has nothing to do, by itself, with the operating conditions of the bulbs. 
2. But a vehicle with CAN bus is more likely to be monitoring everything it can by using sensors throughout the car that communicate to the status monitoring system via CAN bus. These sensors are currently not part of the bulb, but may be built into the lamp housing. Or they may be further back in the wiring harness. 
3. The annoying diagnostics caused by fitting low power lights do not have any inherent effect on the operation of the lights themselves, but there is also a possibility that a CAN bus controller will someday be designed to take action based on the sensor inputs and/or to vary the power to the light. Or even someday expect the light to include its own sensors and active controls.


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## protivakid

Again thanks for all the replies guys... I just wish someone had a concrete answer as to why the LED sale site would say not to do this.


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## SemiMan

protivakid said:


> Again thanks for all the replies guys... I just wish someone had a concrete answer as to why the LED sale site would say not to do this.




Ask them.


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## protivakid

I did but I figured the experts here would know better than the tech support of the company selling them. They replied saying basically that the CAN-Bus bulbs just have a shorter life than a normal LED because of the increased heat an such. Based on this it seems the warning on their site is more to protect them and their 2-year bulb warranty so people are not sending bulbs back constantly when they burn out. They said if bulb failure was not a concern of mine it should work fine. No mention of any risk of fire or anything.

If anyone else here has info please chime in.


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## bshanahan14rulz

Car looking for a 10W load, only sees a 0.25W load, assumes bulb is bad. Makers of the LED bulb put in a resistor to burn up 9.75W, car now sees a 10W load. But also, resistor is putting out 9.75W of heat. 

These numbers are made up, but you get the idea.


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## mesa232323

Being a former ASE certified master Volvo technician I might be able to give some insight. I've worked on plenty of control area network vehicles and never bothered to measure the output voltage to the light. You pretty much grasp the idea of CAN communications on the vehicle except that the car isn't just monitoring the LED, but is supplying the LED with power from a "computer" as apposed to a simple circuit system using relays and switches directly connected to the battery +. That being said, the light controlling "computer" may have an output voltage of 5.0v or less. CAN bus vehicles also use pulse width modulation so that LED would be regulated on a CAN bus vehicle and may overheat when directly connection to the battery.


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## pcesarmc

The control center is probably just monitoiring a bit from some tranceiver that is able to identifiy if the bulb is driving current or not. That transceiver is for sure working with the current levels of a incandescent bulb.
Have a built in resistor should not be a big problem for the small lamps with small power but for sure is not the same for the high power lamps (turn signal, brake, etc) since they will need to dissipate a lot of heat over its builtin resistor. For sure the lifetime of the LED will be afected. Under this point ov view, is preferable to have the load resistor externaly.
Another think tha none is taking car of is: By using a load resistor there will not be any alarme in the case of fail in the LED since de resistor will still be there, working and driving the current like a incandescent bulb......

Paulo Cesar


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## ESELEM

inetdog said:


> To restate and summarize what has been said so far:
> 
> 1. The presence or absence of CAN bus electronics in the car has nothing to do, by itself, with the operating conditions of the bulbs.
> 2. But a vehicle with CAN bus is more likely to be monitoring everything it can by using sensors throughout the car that communicate to the status monitoring system via CAN bus. These sensors are currently not part of the bulb, but may be built into the lamp housing. Or they may be further back in the wiring harness.
> 3. The annoying diagnostics caused by fitting low power lights do not have any inherent effect on the operation of the lights themselves, but there is also a possibility that a CAN bus controller will someday be designed to take action based on the sensor inputs and/or to vary the power to the light. Or even someday expect the light to include its own sensors and active controls.



You're mostly right here, but you need to go even further with this line of thinking.

At least in the modern vehicles I'm the most familiar with, the CAN bus, if it has one, has _nothing_ to do with monitoring the status of any of the light bulbs in the car. Individual sensors are unlikely to be tied directly into the CAN bus of a vehicle. This is because, for something to be tied into the CAN bus, it has to have the ability to communicate on the CAN bus. It's expensive to give each and every sensor the necessary communication hardware to send and receive CAN messages.

In reality, most sensors report directly back to a module through any number of electrical signals (_not_ CAN messages). From there, the module either acts directly on the signal, or if necessary, converts that sensor's reading into a network message and sends it over the CAN bus to another module.

In the case of light bulbs on a car, they're generally all controlled by just a very few modules, maybe just one. And, if the current through the bulb is actively monitored, it's monitored directly by that module, the same module providing power to the bulb. This is where my knowledge gets spotty, but I believe the output for any bulb that's actively monitored for current flow has a FET transistor on the output circuit to the bulb, and somehow this provides a signal back to the module indicating the current flow through the bulb. So, when you say that the sensor is further back in the wiring harness, that's pretty much correct. It's all the way back directly inside the module that's putting voltage out to the bulb.

Anyway, what it all boils down to is that the same module powering your bulbs is the one that's monitoring them for faults, no CAN bus involved. And furthermore, there's not much of a reason for any module in the vehicle to give a damn about what current your dome light is drawing aside from the module actually powering the dome lamp. So, the current draw of your dome lamp is never going to be encoded into a CAN message and sent over CAN bus, because no one else cares how your dome lamp is doing. (Well, ok, that module might send out a general CAN message saying "dome lamp burned out" so the cluster will display a message for you telling you it's burned out, but that's about it.)



So please, let's all stop calling it a CAN bus bulb. It's a ridiculous term, and it's making my head hurt.


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## vmaldia

an example given is a car designed for a 5w incandescent but the CANBUS minimum threshold is around 2w so the LED bulb is 0.7w plus resistors to increase the wattage to 2w

http://ledchoice.eu/en/making-led-bulbs-can-bus-friendly.html


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## dno36

OK all,
I realize this is an older thread, however I have a relative question.
If I have a Non-CANBus vehicle, is there any advantage to using a CANBus bulb in a Non-Flashing application, like dome, dash, map, back-up, CMHSL's or similar??
The CANBus bulbs are a bit more expensive, would there be any advantage or reason to buy them?
Thanks in advance


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## Redd

It has been a long time since we were taught to build flashlights and buzzers in grade school and I learned about Ohm's Law and Magic Smoke shortly after that. As others have suggested, a vehicle with a CANBUS system uses multiple computers to monitor multiple systems. The Germans especially seem to take joy in monitoring the exterior lights on a car. (Cadillac used fiber optics back in the 70's so the driver could actually SEE if the bulbs were on!)

The way these systems work is by sensing the amount of power that the bulb socket is drawing, and that in turn depends on the resistance of the bulb assembly. Whether it is tungsten or halogen or LED, it has a specific resistance range. When a tungsten bulb burns out, the resistance is infinite and the current (power) consumption is zero. When the bulb is "cold", but good, it will have a very low but real resistance, which changes as the bulb turns on and the filament starts to glow. For a "20 watt, 12 volt" bulb, Ohm's Law tells us that power equals voltage times current, so 20 watts of power at twelve volts will mean the bulb is drawing about 1.6 amps and has a resistance of 7.2 ohms. (Google Ohm's Law, it calculates a lot of these relationships.) Actually, the bulb will draw different amounts of power at 14.4 volts, running the engine, than it does at 12 volts, engine off, as well. 
But an LED? The resistance changes radically depending on the direction (polarity) of the voltage. And the LED works differently, it only wants to see a specific voltage, like three volts, and anything more blows it out. So either you gang several up (3 x 4 = 12 volts) to share the voltage, or you add load resistors (cheap) or power controllers to restrict the power to the LED (expensive) in other ways. They can get complicated if you're trying to get the real details right. Yeah, any idiot can cook a hamburger, but do you know how to make a really good one? Starting with a real live cow? Right, a little more complicated.
Anyway, some light control computer is looking at that power draw and saying "Gee, this bulb is only drawing 0.2 amps, it should be drwing a full two amps...there must be something wrong here!" and turning on the idiot light. A literal IDIOT LIGHT because it isn't smart enough to understand the change in bulbs.
The entire mystery is because some automakers--mainly the Germans--want to bury you in FUD and convince you there is magic and high technology in their cars (sometimes there is some) instead of just telling you "Yes, our system needs to see a value of five to ten ohms on the bulb socket, or it will throw an error code." Exact numbers vary with each system, many time a 10 ohm load resistor works, sometimes it get more complicated than that.
And plenty of LED vendors are glad to charge you $50 a bulb because they can also pretend there's magic. And they want some profit, for having done the homework. Sometimes.
So, no reason, no advantage, to buy "CANBUS" compatible bulbs, unless you need them. Will they work? Probably. But they won't be any better than any other bulb, and they can fail in more creative ways. Must be dinner time again...don't buy the live cow if you only want a hamburger!


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## xevious

Reviving this old topic, just in case someone here might have some useful info.

CANBUS aggressiveness varies by maker. VW / Audi / Porsche seems to be the most aggressive with this.

I do agree about main headlight applications that substituting LED in place of a reflector system designed for incandescent will be fraught with challenges -- most bulbs won't do the job right (artifacts, dark segments/spots). But in the case of reflector housings for marking & signal use, this generally won't be a problem.

Fooling the CANBUS system requires an LED "bulb" (assembly) that specifically adds a resistor circuit such that the LED bulb draws enough current so that the CANBUS thinks there's a normal working bulb in use. LED bulbs that don't draw enough current will cause CANBUS to throw a bulb-out error. So the solution for this is usually done by adding a resistor. But I have seen some people state that this did not work for them. I presume that either the resistor wasn't sufficient or there is some other characteristic beyond resistance in play.

Since LED's inherently draw significantly less power for the same output as incandescent, one would think that adding more LED emitters to the bulb assembly would help increase the load, to the point of being enough to fool the CANBUS system. The question is, how much wattage is needed? For example, if you have a 5W 194 / T10 incandescent bulb replaced with a 3W LED assembly, would CANBUS still throw an error? Does CANBUS test explicitly for 5W, or does it have a lower threshold?


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## Alaric Darconville

xevious said:


> Reviving this old topic, just in case someone here might have some useful info.


That's quite a threadsurrection-- over three years.



> I do agree about main headlight applications that substituting LED in place of a reflector system designed for incandescent will be fraught with challenges -- most bulbs won't do the job right (artifacts, dark segments/spots).


That's a lot of words to say it just doesn't work.



> But in the case of reflector housings for marking & signal use, this generally won't be a problem.


It's still a major problem, but there are some better examples being made. Still, they don't work in EVERY lamp in which the incandescent version it claims to replace works correctly. 



> Fooling the CANBUS system requires an LED "bulb" (assembly) that specifically adds a resistor circuit such that the LED bulb draws enough current so that the CANBUS thinks there's a normal working bulb in use. LED bulbs that don't draw enough current will cause CANBUS to throw a bulb-out error. So the solution for this is usually done by adding a resistor. But I have seen some people state that this did not work for them. I presume that either the resistor wasn't sufficient or there is some other characteristic beyond resistance in play.


It could be that they didn't use a resistor to simulate a filament bulb properly, or for combination stop and tail lamps only putting the resistor on one of the functions.



> Since LED's inherently draw significantly less power for the same output as incandescent, one would think that adding more LED emitters to the bulb assembly would help increase the load, to the point of being enough to fool the CANBUS system.


Which would take a LOT of LEDs.



> The question is, how much wattage is needed? For example, if you have a 5W 194 / T10 incandescent bulb replaced with a 3W LED assembly, would CANBUS still throw an error? Does CANBUS test explicitly for 5W, or does it have a lower threshold?


It's not really testing the wattage, but the resistance. Too-high resistance looks like open short, which triggers a bulb out indicator (too low resistance could look like a closed short, but often that just leads to a blown fuse).


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