The dreaded bulb warning light. It illuminates your dashboard, signaling a potential issue with your vehicle’s lighting system. For those with a car equipped with the BCMPQ35 module (common in many Volkswagen Group vehicles), and who have retrofitted LED bulbs, this guide will show you how to turn off the bulb warning light using VCDS.
Understanding the BCMPQ35 module is crucial. Contrary to popular belief, this module works with LED bulbs regardless of its revision (LED-ready or not). However, it’s not inherently designed to support LEDs in traditional filament bulb housings, leading to those pesky warning lights.
Bulb monitoring and diagnostics are handled by the BCM, not the CAN bus system. “CANBUS friendly” or “error-free” bulbs are marketing terms. They don’t interact with the CAN bus; “error-free” simply implies a bulb designed to avoid triggering error messages.
Let’s dive into three methods for addressing bulb diagnostics when retrofitting LEDs:
Three Solutions for LED Retrofit Bulb Warnings
1. The Software Approach (VCDS Coding)
This method involves coding the BCM using diagnostic software like VCDS to either disable the bulb diagnostics or adjust their parameters to accommodate the LED’s operating characteristics. This is the cleanest solution, avoiding any physical modifications to your vehicle’s wiring. This is the preferred method for turning off the bulb warning light with VCDS. Specific coding procedures may vary depending on the vehicle and BCM version, so consult reputable VCDS coding guides for your specific application.
2. The Hardware Approach (Resistors)
This involves adding a high-wattage resistor in parallel with each LED bulb. The resistor mimics the electrical load of a traditional filament bulb, preventing the BCM from detecting a fault. However, this can create a wiring mess, generate significant heat, and require careful resistor placement to avoid damage to nearby components. While effective, it’s more complex than the software solution.
3. The “Ignore It” Approach
The simplest approach is to disregard the warning light and any accompanying error messages. While functionally feasible, it’s not recommended as it may mask genuine lighting issues.
LED Retrofit Myths and Realities
A common misconception is that resistors are necessary to maintain the correct turn signal flash rate with LEDs. This was true with older flasher circuits, but the BCMPQ35 module regulates flash rate independently of bulb resistance. Hyper-flashing on the dashboard with LEDs and no coding is a deliberate feature indicating a bulb issue, not a functional problem with the external lights.
Another important note: The BCM might seemingly accept coding changes (like DRL dimming) but not implement them while error codes are present. Clearing Diagnostic Trouble Codes (DTCs) after reverting to standard bulbs can resolve this issue. Disabling bulb diagnostics via VCDS coding can prevent further complications when using LED replacements.
In conclusion, turning off the bulb warning light after an LED retrofit in a vehicle with a BCMPQ35 module is best achieved through VCDS coding. While other methods exist, software modification provides the cleanest and most effective solution. Remember to consult reliable resources and coding guides specific to your vehicle and BCM version for detailed instructions.
