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2019 S5 DRL Flickering & Headlight Warning - B100A Code

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Sarah K. · rep 0 · May 22, 4:26 AM · 1 replies · solved · Question

Vehicle: 2019 Audi S5 Coupe

Hey everyone,

I'm having a weird issue with the driver's side DRL (Daytime Running Light) on my 2019 Audi S5 Coupe. It's started flickering intermittently, almost like it's struggling to stay on. Sometimes it's fine, but then it'll start flickering rapidly, and occasionally it just goes out completely. When it goes out, I get a 'Headlight System Malfunction' warning on the dash.

The passenger side DRL and both main headlights seem to be working perfectly fine. I've checked the connections I can see, but everything looks secure. I ran a scan and got a B100A code, which my scanner says is a 'Headlight Control Module Fault'.

Could this be a faulty LED driver, or is the entire headlight control module on its way out? Has anyone else experienced this with their S5 or other Audi models with LED headlights? Any advice would be great!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:26 AM

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ClearTheCode admin answer:

The B100A code (Headlight Control Module Fault) combined with your flickering DRL and headlight warning strongly points to an issue within the headlight assembly's electrical components. Modern Audi LED headlights are complex, often integrating the LED driver and control module directly into the headlight unit.

Potential Causes:

  1. Faulty LED Driver/Module: The most likely cause. The LED driver, which regulates power to the DRL LEDs, can fail internally, causing flickering or complete failure. In many Audi models, this is part of or closely integrated with the main headlight control module.
  2. Internal Wiring Harness Damage: Within the headlight assembly, internal wiring can become damaged or corroded, leading to intermittent connections to the DRL LEDs.
  3. Moisture Ingress: If moisture gets inside the headlight housing, it can corrode electrical components and connections, leading to malfunctions.
  4. Power Supply Issues: While less likely for a single DRL, a fluctuating power supply to that specific headlight module could cause issues.

Troubleshooting Steps:

  1. Visual Inspection: Carefully inspect the exterior of the headlight for any signs of cracks, condensation, or damage that could indicate moisture ingress. Also, check the main electrical connector going into the back of the headlight assembly for corrosion or looseness.
  2. Swap Modules (if possible): If your S5 has separate, accessible LED drivers or control modules for each headlight, you might be able to swap them (left to right) to see if the fault moves. This can help confirm if the module itself is the problem. Note: This is often not easily done without specialized tools or significant disassembly.

When to See a Shop:

  • If the visual inspection doesn't reveal any obvious issues.
  • If you cannot easily access or swap components.
  • A professional diagnostic scan with Audi-specific tools is essential. These tools can communicate directly with the headlight control module, read specific fault codes related to the DRL circuit, and even test individual LED segments. Often, the entire headlight assembly or a specific control unit within it needs replacement. Due to the complexity and cost of modern LED headlights, professional diagnosis is highly recommended to avoid replacing the wrong component.
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