Quick preface, it is a common misconception that Dodge, Jeep, Ram and Chrysler vehicles have a CANbus CPU but this is not true. Most 05+ and some older model Chrysler family vehicles are equipped with a TIPM CPU or Totally Integrated Power Management CPU. In most cases, a CANbus certified lighting solutions will not function properly on a TIPM CPU equipped vehicle.
According to Wikipedia, the CANbus CPU or Controller Area Network (CAN bus)
is a robust vehicle bus standard designed to allow micro-controllers
and devices to communicate with each other in applications without a
host computer. Of particular relevance is the checks it runs on the headlights and sometimes fog lights.
So what does this mean to those looking to convert their headlights to HID or LED?
It means your vehicle's CPU type matters and should be determined prior to purchasing any after-market 12v electronic including headlight and fog lights.
If you have a CANbus CPU equipped vehicle then it would be wise to have a relay and ECM capacitor set on hand or ensure you add the "Relay Bundle" to your purchase; especially, if the HID conversion kit you plan to install is not CANbus certified. If the HID kit is CANbus certified then you can complete a full installation without either accessory; however, a relay is always a good idea because it improves efficiency, product life and to a small degree brightness.
Why do I need a relay and/or capacitors if I plan to install a non-CANbus certified lighting solution in my CANbus equipped vehicle?
In the simplest terms, the CPU scans the headlight circuit and as long as the electrical signal/feedback is within acceptable parameters (designed for halogen) it will register the headlights as working properly.
The problems arises when introducing a non-CANbus certified HID or LED kit, due to the improved efficiency and lowered electrical draw of these lighting solutions the CANbus CPU often registers a fault and activates the BOW (Bulb Out Warning) and in some cases shuts off the headlights completely.
In order to pass the headlight check and prevent these fail-safe measures from throwing the BOW light or shutting off the headlights we need to manipulate the electrical signal/signal, enter the capacitor.
The CANbus tuned capacitor; specifically, manipulates the electrical signal/feedback essentially tricking the CPU into registering that the halogen bulb is still installed and working properly.
CANbus certified lighting solutions come equipped with an internal or external CANbus decoder/capacitor that if finely tuned to ensure that the electrical signal of the HID or LED kit returned back to the CPU is within the established parameters resulting in a successful HID conversion.
So how do I determine if my vehicle has a CANbus CPU?
As a general rule of thumb most 00+ European makes like Mercedes, BMW, Audi, Mini, etc...are CANbus CPU equipped. However, CANbus as technology is being adopted by most modern vehicle manufacturers and being equipped in many new vehicles like late model Silverado, Sierra, Elantras etc...