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.
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.
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.
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.