Thinking about upgrading the rear lights on your MK6 Golf GTI to the sleek, modern look of OEM LED tail lights? It’s a popular modification, and for good reason. LED tail lights can dramatically enhance the appearance of your Golf, bringing a touch of contemporary styling to even earlier models. However, retrofitting them, especially on a pre-facelift model initially equipped with standard halogen lights, isn’t always a straightforward plug-and-play process. This guide dives into the viability of this retrofit, specifically for a UK-spec 2009 MK6 Golf GTI, addressing common concerns around Body Control Module (BCM) compatibility, coding intricacies, and potential pitfalls.
Decoding the Body Control Module (BCM) for LED Tail Light Compatibility
One of the first hurdles in retrofitting Mk6 Golf Tail Lights is understanding your car’s Body Control Module (BCM). The BCM is essentially the brain controlling various electrical functions in your vehicle, including lighting. For LED tail lights to function correctly, your BCM needs to be compatible, both in terms of hardware and software.
BCM Software Version and Midline vs. Highline: What’s the Minimum?
You’ll often encounter discussions about minimum BCM software levels, with figures like 500 or 575 being cited as necessary for LED tail light compatibility. Furthermore, the terms “Midline” and “Highline” BCM are frequently mentioned, adding another layer of complexity. The original poster’s BCM is identified as:
Part No SW: 1K0 937 086 C
HW: 1K0 937 086 C
Component: BCM PQ35 M 103 0537
Revision: 00103 ACThis indicates a “Midline” BCM (denoted by the “M” after PQ35) with software revision 537. While some sources suggest a minimum software level of 500 might suffice, others recommend 575 or even a Highline BCM.
Alt text: Close-up of a Midline BCM label, highlighting “PQ35 M” to identify the BCM type.
The confusion often arises because different BCM versions and software levels have varying capabilities. Highline BCMs generally offer more features and broader compatibility with advanced vehicle functions, including LED lighting. Midline BCMs, while capable, might have limitations depending on their software revision.
Dealer Insights vs. Real-World Experience
Interestingly, the original poster was informed by a VW dealer that their car, at the time of production, should have had a 1K0 937 087 E BCM – a Highline version. This discrepancy highlights a common issue: dealer information isn’t always definitive for retrofitting scenarios. While the dealer’s statement might point towards the ideal BCM for LED tail lights, it doesn’t necessarily mean a Midline BCM with a sufficiently high software revision can’t work.
eBay searches for 1K0 937 087 E BCMs often reveal units with software revision 575, further fueling the idea that this higher software level is indeed desirable for LED compatibility.
Decoding Byte 18: The Key to LED Tail Light Coding
Assuming your BCM is capable, the next crucial step is understanding and correctly coding Byte 18 within the BCM settings using VCDS (VAG-COM Diagnostic System) or similar diagnostic tools. Byte 18 essentially tells the car’s electrical system what type of lighting is installed, front and rear.
Understanding Byte 18 and Avoiding Bulb Out Errors
The infamous “Byte 18 club” refers to the challenges and uncertainties surrounding coding this specific byte. The issue stems from VCDS not being able to display the actual current coding value of Byte 18, often showing “00” instead. This makes it difficult to revert to the original setting if things go wrong.
Based on the original poster’s car configuration (halogen front DRLs and halogen rear lights), the expected Byte 18 value is “02”:
- 02: VW360 Halogen VW360 RdW TFL_0 ROM 2 VW360 VW360 halogen RdW TFL_0 Rom 2
For retrofitting LED rear lights while retaining halogen front DRLs, the commonly suggested new Byte 18 value is “15”:
- 15: VW360 GTI Halogen “VW360 RdW TFL_0 +LED SBBR” ROM 21 VW360 GTI halogen “VW360 RdW TFL_0 + LED SBBR” ROM 21
Alt text: Screenshot of VCDS software interface, showing Byte 18 coding options for vehicle lighting configuration.
However, simply changing Byte 18 to “15” isn’t always a guaranteed fix. Variations in BCM software, the specific LED tail light units, and even regional vehicle specifications can influence coding requirements. There’s often an element of trial and error involved in achieving correct coding and preventing “bulb out” errors on the dashboard.
BCM Revision: Half the Battle?
The BCM revision level plays a significant role in the success of Byte 18 coding. A higher software revision, particularly in a Highline BCM, is more likely to have the necessary firmware and coding parameters to correctly recognize and operate LED tail lights without errors. Therefore, having a compatible BCM is indeed “half the battle” in ensuring a smooth and successful LED retrofit.
“Get Out of Jail Free” Card Options: Planning for Reversibility
The fear of “bricking” your car’s electrical system during a DIY modification is understandable, especially for daily drivers. Fortunately, there are strategies to mitigate risks and ensure reversibility if the LED tail light retrofit doesn’t go as planned.
BCM Removal and Original Coding Retention
A key question is whether the original BCM retains its coding when removed from the car. The answer is generally yes. BCMs store their coding in non-volatile memory, meaning the settings are preserved even without power. This is a crucial safety net. If the LED retrofit fails, you can theoretically reinstall your original halogen tail lights and your original BCM, and the car should revert to its previous lighting configuration.
Alt text: Image of a BCM unit detached from its vehicle mounting, emphasizing the physical module itself.
Installing and Coding a New or Used BCM
Upgrading to a Highline BCM with a higher software revision can be a proactive step to increase the chances of a successful LED retrofit. While installing a new or used BCM is more involved, it offers greater flexibility and future-proofing.
Coding a new BCM can be done using VCDS. While you can’t directly “paste” coding from a Midline to a Highline BCM, the process typically involves taking screenshots of the coding parameters in your original BCM and manually replicating them in the new Highline BCM. There are also resources and guides available online that provide base coding settings for Highline BCMs in MK6 Golfs.
Dealer Assistance: The Last Resort?
In a worst-case scenario, could a VW dealer revert your car back to its original lighting settings if the retrofit goes wrong? Theoretically, yes. Dealers have access to factory diagnostic tools and databases that should allow them to recode the BCM and restore the original vehicle configuration. However, their familiarity with retrofitting scenarios and the “Byte 18 problem” might vary. It’s always best to inquire beforehand about their experience with such modifications.
Conclusion: Proceed with Caution and Preparation
Retrofitting MK6 Golf tail lights is a desirable upgrade, but it requires careful planning and research. Understanding your BCM, correctly coding Byte 18, and having a backup plan are crucial for a successful outcome. While a Midline BCM might work, upgrading to a Highline BCM with a higher software revision is generally recommended for optimal compatibility and reduced risk of coding issues.
Before embarking on this project, thoroughly research your specific car’s BCM, gather information from online forums and communities, and consider consulting with experienced individuals or workshops specializing in VW retrofits. With proper preparation and a methodical approach, you can successfully enhance the look of your MK6 Golf with stunning LED tail lights. And remember, resources like obd-de.com are valuable tools for understanding your car’s diagnostics and coding parameters, empowering you to tackle such upgrades with greater confidence.
