The BCMPQ35 module controls lighting functions in many 2012 Volkswagen Jettas. Understanding this module is crucial for retrofitting LED headlights without triggering error messages. This guide explains how to enable the headlight circuit for LED bulbs using VCDS.
Understanding the BCMPQ35 Module and LED Compatibility
Contrary to popular belief, the BCMPQ35 module’s revision (LED-ready or not) doesn’t prevent using aftermarket LED bulbs. The “LED-ready” designation applies to factory-installed LED options, not retrofitted bulbs in standard housings. Any BCMPQ35 will technically power LEDs, but the challenge lies in bypassing the bulb monitoring system.
Bulb Monitoring and Diagnostic Solutions
The BCMPQ35, not the CAN bus system, handles bulb diagnostics. “CANBUS friendly” bulbs are a misnomer; “error-free” bulbs are more accurate. Here are three solutions to avoid bulb-out warnings when using LED retrofits:
1. Software Coding (Recommended):
This “clean” approach modifies the BCM’s coding to disable or adjust bulb diagnostics for LED characteristics. This requires specialized software beyond VCDS, offering a solution without physical modifications. This is the preferred method for a clean, error-free installation.
Example of a VCDS coding screen.
2. Hardware Resistors:
Wiring a high-wattage resistor in parallel with each LED bulb simulates the load of a filament bulb, preventing error messages. However, this can lead to a complex wiring setup and significant heat generation. Resistors need careful placement to avoid damaging surrounding components. While effective, this method can be cumbersome. Choose resistors with appropriate wattage ratings to avoid overheating.
Example of a resistor installed in a vehicle wiring harness.
3. Ignoring Error Messages:
The simplest approach is to disregard the bulb-out warnings on the multi-function display (MFD). This requires no technical expertise but comes with the constant annoyance of error messages.
LED Retrofit and Flash Rate Considerations
The BCMPQ35’s flash rate is independent of bulb resistance, unlike older flasher circuits. While hyper-flashing might appear on the dashboard with uncoded LEDs, the external lights will flash at the correct rate. This internal hyper-flashing acts as a visual cue for a potential issue, especially with bulb diagnostics disabled.
Troubleshooting BCM Coding Issues
Sometimes, the BCM might appear to accept coding changes (e.g., DRL dimming) but not implement them while error codes are present. Clearing diagnostic trouble codes (DTCs) and reverting to standard bulbs temporarily can resolve this issue. Disabling bulb diagnostics entirely often eliminates further complications with LED retrofits.
Example of clearing DTCs in VCDS
Conclusion
Successfully enabling the headlight circuit for LED bulbs in a 2012 Jetta with a BCMPQ35 module depends on understanding the bulb monitoring system. While software coding provides the cleanest solution, hardware resistors and ignoring errors are alternatives with their own trade-offs. Understanding these options allows for informed decisions when retrofitting LED headlights.
