Complete Guide to Headlights on the Mercedes-Benz W166

Benz Headlights

Introduction

Headlights are not just a vital safety feature—they also contribute heavily to the look and identity of a vehicle. The Mercedes-Benz W166 platform, which includes the ML-Class, GL-Class, and later the GLE-Class (2012–2019), features a range of sophisticated headlight systems designed to enhance visibility, safety, and styling. As an experienced electrician technician specializing in Mercedes-Benz vehicles, I’ve had hands-on experience diagnosing, repairing, and upgrading the W166’s headlight systems. In this post, I’ll walk you through everything you need to know about them, from their design to common issues and repair options.

Types of Headlights Used in the W166

Depending on the trim level and production year, the W166 series came equipped with one of the following headlight systems:

1. Halogen Headlights (Base Models)

  • Basic functionality
  • Manual leveling
  • Simple bulbs
  • No dynamic features or LED components

2. Bi-Xenon Headlights with LED DRLs

  • High-intensity discharge (HID) lighting for both low and high beams
  • Integrated LED daytime running lights (DRLs)
  • Auto-leveling and headlight washers (optional)
  • Optional Active Curve Illumination for better cornering visibility

3. Full LED Intelligent Light System (ILS)

  • Available on higher trims and AMG models
  • Fully LED-powered low and high beams
  • Adaptive lighting with auto high beam assist
  • Cornering function and weather mode
  • Integrated LED DRLs, turn signals, and side marker lights

Components of the W166 Headlight System

Understanding the individual components helps diagnose and repair headlight issues:

  • Headlight Control Module (HCM): Regulates power and signal logic to the lighting elements
  • LED Driver Module: Powers individual LED elements in ILS systems
  • Ballast/Igniter: Used in Bi-Xenon systems to ignite and sustain the arc in HID bulbs
  • Level Sensors: Found on vehicles with auto-leveling, connected to the suspension
  • DRL/Position Lights: Usually LED-based and integrated into the headlamp housing
  • Headlight Switch (in cabin): Connects via /CAN bus to trigger lighting states

Common Headlight Problems on the W166

1. Headlight Not Working (One Side)

  • Cause: Faulty bulb, blown fuse, or defective ballast
  • Fix: Replace bulb or ballast, check power supply at connector

2. LED DRL Strip Not Functioning

  • Cause: Failed LED driver module or burnt-out LEDs
  • Fix: Replace entire module or headlight unit (LEDs are often non-serviceable)

3. Water or Moisture Inside the Headlight

  • Cause: Damaged seal or cracked housing
  • Fix: Dry and reseal the unit or replace the headlamp assembly

4. Headlight Flickering or Intermittent Function

  • Cause: CAN bus communication issues or failing ballast/module
  • Fix: Diagnostic scan, check grounds and power, update software if needed

5. Headlight Leveling Error Warning

  • Cause: Faulty level sensor or wiring issue
  • Fix: Replace sensor, reprogram module using STAR diagnostic tool

Diagnosing Headlight Issues

When diagnosing a headlight issue in the W166:

Step 1: Visual Inspection

  • Check connectors, wiring, and fuses
  • Inspect for moisture or physical damage

Step 2: Use Diagnostic Tools

  • Connect  STAR diagnostic system
  • Read fault codes from the SAM (Signal Acquisition Module) and HCM
  • Run actuator tests on headlight functions

Step 3: Measure Voltage and Ground

  • Confirm voltage at the headlight connector
  • Test continuity on ground circuits

Step 4: Module Reprogramming

  • In case of software glitches or retrofit installations, module coding or updates may be required

Headlight Replacement and Upgrades

  • Halogen to Xenon/LED Upgrade: Requires wiring modifications, headlight control module swap, and coding
  • Replacing a Xenon Bulb or Ballast: Always use OEM or equivalent parts for proper beam performance
  • Replacing Complete Headlight Assemblies: Requires careful calibration and module pairing

Tips for Headlight Maintenance

  • Clean headlights regularly to maintain lens clarity
  • Avoid aftermarket HID kits that may overload circuits
  • Use dielectric grease on connectors to prevent corrosion
  • Don’t ignore headlight warnings on the dash—they may indicate deeper electrical faults

Conclusion

The headlight systems in the Mercedes-Benz W166 are sophisticated, combining style, safety, and functionality. Whether you have basic halogens or the advanced Intelligent Light System, understanding how the system works and what components are involved can save you time and money.

As a professional Mercedes-Benz electrical specialist, I provide full diagnostic and repair services for W166 headlight systems, including:

  • LED and Xenon troubleshooting
  • Module coding and replacements
  • Moisture repair and resealing
  • Upgrades from halogen to LED/Xenon systems

If your W166 is having headlight issues or you’re considering an upgrade, contact me today for expert, reliable service tailored to your Mercedes-Benz. Contact Mercedes Benz engineer Abuja 09015329867