If you’re experiencing a Vcds Bulb Warning after retrofitting LED lights in your vehicle with a BCMPQ35 module (common in VW and Audi models), this guide will provide solutions. The BCMPQ35 module controls various lighting functions and diagnostics, including bulb monitoring. Understanding how this module interacts with LEDs is crucial for a successful retrofit.
BCMPQ35 Module and LED Compatibility
Contrary to popular belief, the BCMPQ35 module’s revision (LED-ready or not) doesn’t prevent LED bulb installation. Any revision will technically work. However, the module isn’t designed for LEDs in traditional housings, leading to bulb warning errors. “LED-ready” BCMs are specifically for factory LED options, not aftermarket retrofits.
Understanding Bulb Monitoring and the VCDS Bulb Warning
The BCMPQ35 module performs bulb monitoring and diagnostics, not the CAN bus system itself. “CANBUS friendly” or “error-free” bulbs are marketing terms. The actual issue is the module detecting the lower current draw of LEDs and triggering a VCDS bulb warning.
Three Solutions for VCDS Bulb Warning After LED Retrofit
There are three primary ways to address the VCDS bulb warning triggered by LED retrofits:
1. Software Coding (The Clean Solution)
This method involves using diagnostic software (other than VCDS) to modify the BCMPQ35’s coding. You can either disable bulb diagnostics entirely or adjust the parameters to accommodate the LED’s operating characteristics. This provides a clean solution without physical modifications to the wiring.
2. Hardware Resistors (The DIY Approach)
This involves adding a high-wattage resistor in parallel with each LED bulb. The resistor mimics the resistance of a traditional filament bulb, preventing the VCDS bulb warning. However, this can lead to a complex wiring setup and significant heat generation. Resistors must be appropriately rated (50W for a 21W bulb) and carefully placed to avoid damage. Despite marketing claims, these are not “CANBUS cancellers” or “decoders.”
3. Ignoring the Warning (The Simple Approach)
The simplest approach is to disregard the VCDS bulb warning and any accompanying error messages on the multi-function display (MFD). This requires no special skills or tools. However, you will have to tolerate the warning light.
LED Retrofit and Flash Rate: A Common Misconception
The BCMPQ35 module does not rely on bulb resistance for flash rate control like older flasher circuits. Hyper-flashing on the dashboard with LED indicators is a deliberate feature indicating a bulb issue, not a true hyper-flashing condition. The external lights will flash at the correct rate. Disabling bulb diagnostics via coding will eliminate this dashboard hyper-flashing.
Important Considerations for BCMPQ35 Coding
When making coding changes to the BCMPQ35, clear any existing Diagnostic Trouble Codes (DTCs) first. Sometimes, the module might appear to accept coding changes (like DRL dimming) but not implement them while error codes are present. Clearing DTCs and returning to standard bulbs temporarily can resolve this issue before disabling bulb diagnostics.
