In this post, we’re bringing you an episode of ABD TV where we aim to answer all of those burning questions, clear up the confusions and leave you brimming with knowledge.
Today we are tackling the murky waters of LED bulbs, more specifically the hassles of the dreaded CANbus error codes.
So what do I mean with CANbus Error Codes?
Well more modern vehicles are all about sensors, warnings and messages. When something goes wrong on your car, you’ll often get some sort of notification of this on your dash. This could be a simple warning light illuminating, or an actual written message.
Your car is full of these sensors and they will monitor many many systems throughout your vehicle from fuel injection to brake pads to seat belts.
In the case of bulbs, your car will let you know when one of the exterior applications has failed. This checking/reporting is commonly referred to as a CANbus system.
Of course these error messages are very useful and a great addition to modern vehicles, so what’s the problem?
Aftermarket LED Bulbs causing Error Codes
The problem is with false positives created with aftermarket products such as LED bulbs.
The most common way a canbus system will check if a bulb is working or not is to measure the resistance on the circuit. Some vehicles measure the total circuit resistance, others check individual bulbs. But they are checking for the characteristics of a normal filament bulb.
One of the core selling points of an LED bulb is the lower power draw. Who doesn’t want an extra bit of fuel saving! Especially with the likes of caravans and motor-homes.
I won’t bore you with the physics here, but less power means there is more resistance (P=V²/R). Your vehicle CANbus system is therefore going to see something it’s not expecting and flag up the error message. In some cases it will even cut power to that circuit, meaning your perfectly good LED bulb fails to illuminate.
Fixing the Error Codes
There are 2 main ways to overcome this problem and I’m going to run through both of these below:
CANbus Compatible LED Bulbs
The first and most simple solution is to fit a CANbus compatible bulb.
Bulbs like the Twenty20 Cree LEDs and some of the Ring Premium range have additional resistors built into them to adjust the characteristics of the bulb. This brings them closer to the parameters that your car is looking for.
As these are a direct replacement for your existing bulbs, these would always be our first recommendation of what to try.
In 95% of cases, this will be enough to overcome the issue. However some vehicles can be particularly fussy and they still throw up an error.
The issue is with the amount of resistance that would be needed for it to match a filament bulb. It would simply be too big and be too hot. The heat from a resistor would cause it to fail almost instantly.
Therefore the manufacturers can only try and get as close as they can and hope it falls within the required levels.
In cases where you simply have a super fussy vehicle, and even CANbus LED bulbs don’t cut it, we have to move onto our second option and add the resistance another way.
Resistor Kits for LED Bulbs
This is where resistor kits like this one from Osram come in.
This might sound like it’s getting complex but it’s actually very straight forward. You can see how this is done in the video at the top of the page. But the general concept is as follows:
A typical bulb holder that you would have in your car will have 2 wires going to it to supply the power. One for the positive and one for the negative. It’s not important in this case to know which is which, just that you have the correct 2 wires for your LED bulb.
On our resistor, conveniently enough, we also have 2 wires.
Simply use the supplied scotch locks to splice together one leg of the resistor to one bulb holder wire, and the other leg to the other. This is called connecting in parallel.
Once done, this adjusts the resistance to the correct amount without it impacting on the bulb itself.
And that’s it, simple.
Now you are an expert on LED bulbs and canbus issues. Remember, if you have a modern car with a CANbus system, first try a CANbus compatible bulb. If that doesn’t work, break out the resistors and you’ll be up and running in no time.
If you have any questions on this, feel free to ask them in the comments below.
Also if you have any other general product questions you’d like to see us cover in a future ABD TV episode, please send them in either via our social media accounts or via email.