For anyone visiting this thread looking for an answer regarding retrofitting LEDs, here's what you need to know if you have a car equipped with the BCMPQ35 module (as with the original post).
The ...
If you're wanting to fit retrofit LED bulbs rather than the dedicated clusters available from the likes of Hella it doesn't matter if you have an LED-ready revision or not.
ANY will work with LED bulbs (ignoring bulb-monitoring issues for a moment).
LED-ready BCMs are for those cars where factory LED options are available (later Golf 6, Scirocco etc.).
An LED-ready BCMPQ35 is not designed to support LED bulbs fitted in traditional filament bulb housings.
Bulb Monitoring
For clarity, bulb monitoring and diagnostics are performed by the . This is not a function of CAN which is a networking communication standard using a bus topology. "CANBUS friendly" is utterly meaningless marketing blurb while "error-free" accurately describes a bulb design. More on this in a moment.
There are three ways of dealing with existing bulb diagnostics when retrofitting LED bulbs.
The software route involves coding the so diagnostics are either disabled or adjusted to take into account LED operating characteristics. This involves software other than . Those wanting a "clean" solution without physical modifications will want to try this.
The hardware route involves the addition of a high-wattage wire wound resistor in parallel with every retrofitted LED. This could become a wiring mess if the intention is to replace every bulb, and these resistors get HOT. I routinely solder with a 25W iron, a resistor correctly specced for a 21W bulb ideally needs to rated for double this in continuous applications and the nearest common value is 50W. Every bulb you fit will require a wire wound resistor and these will require careful placement to avoid melting nearby plastic components. This is a good solution for those with some DIY and soldering experience but without access to potentially expensive diagnostic software. Referring back to CAN bus, some resistors are sold as "CANBUS cancellers" and "CANBUS decoders". Again, this is meaningless marketing rubbish, they don't "cancel" CAN bus or "decode" it in any way, they merely provide a load to the lighting circuit similar to that of a filament bulb.
Finally, the mindware route involves ignoring the bulb warning and accompanying MFD error messages. This requires no software or DIY skills.
A full LED retrofit without errors or resistors is possible with the BCMPQ35 purely through coding, I know because I've done it. One interesting thing about this module and LED retrofits is many people still think resistors are required to maintain a correct flash rate. This was true with old designs of flasher circuit that relied on the bulb resistance for the correct flash rate, but it's not true with this module. Without coding or resistors you will see hyper-flashing on the dashboard but the lights will be operating externally at the correct rate. This seems to be a deliberately engineered feature to remind you there is an issue with the indicators because with bulb diagnostics disabled there is no hyper-flashing internally either.
One other thing I found in my experiments was at one point my would appear to accept coding changes (DRL Dimming Factor was one) but the change wouldn't take while the was showing error codes. The coding was reporting correctly (LED fogs running at 10%) but there was no output and changing this value didn't make a difference. Returning bulbs to standard and clearing resolved this issue, and since disabling bulb diagnostics there have been no further quirks of fitting LEDs as replacements to the factory originals.
