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Ford DRL Turning Yellow? How to Fix Yellow or Dim LED Daytime Running Lights
A yellow, dull or discoloured daytime running light on some Ford headlights is often assumed to mean the LED DRL module has failed.
That is not always the case.
On some Ford Transit Custom, Ford Fiesta and Ford Puma headlights, the LED module can still be working correctly while the clear acrylic light guides inside the headlight have become burnt or discoloured where they meet the LEDs.
If the damage is limited to the ends of the light guides, it may be possible to repair the headlight by carefully removing the burnt surface.
What Causes the DRL to Turn Yellow?
The LED module shines directly into clear acrylic light guides inside the headlight.
These guides carry the light from the LED through the DRL section of the lamp.
Over time, the ends of the acrylic can become heat damaged. The clear surface can turn yellow, brown, cloudy, blackened or scorched.
Instead of allowing the white LED light to pass cleanly into the light guide, the damaged plastic alters and reduces the light output.
This can make the DRL appear yellow, orange or considerably dimmer than the opposite headlight.
Check the Light Guides Before Replacing the LED Module
Before replacing the DRL module, remove it from the rear of the headlight and inspect the ends of the acrylic light guides.
They should be clear.
If the ends are brown or burnt like those shown in the photos above, the light guide itself is contributing to the yellow or dull DRL.
Replacing the LED module alone will not repair a burnt light guide.
A new module will still be shining through the damaged acrylic.
If the LED module appears to be working correctly, the light-guide ends should be repaired first and the headlight retested.
How to Repair Burnt Ford DRL Light Guides
If the damage is only on the surface of the acrylic, the burnt material can be carefully sanded away until clean acrylic is exposed.
A small rotary multi-tool such as a Dremel makes the job easier.
1. Remove the DRL Module
Switch the lights and ignition off and allow the headlight to cool before working on it.
Gain access to the rear of the headlight and remove the DRL LED module.
Take care not to damage the electrical connector or surrounding headlight components.
2. Inspect the LED Module
Check the LEDs and circuit board for obvious signs of damage.
- Burnt LEDs
- Blackening
- Heat damage
- Discolouration
- Damaged electrical components
If the module is visibly damaged, it should be replaced.
If the module appears serviceable, continue by inspecting the light guides.
3. Inspect the Acrylic Light-Guide Ends
Look into the openings where the LEDs sit against the light guides.
A healthy light guide should have a relatively clean, clear end.
If the surface is brown, yellow or blackened, carefully removing this damaged layer can restore the amount and colour of light entering the guide.
4. Carefully Sand Away the Burnt Surface
Use a small sanding attachment on a rotary multi-tool.
Use a low speed and remove the damaged material gradually.
The aim is simply to remove the burnt surface until clean acrylic is visible again.
Do not unnecessarily shorten the light guide or significantly alter its shape.
Only remove as much material as required to reach clean plastic.
5. Keep Sanding Dust Out of the Headlight
This part is important.
Sanding the acrylic will create fine plastic dust, and you do not want this entering the headlight.
Use a vacuum or suitable extraction alongside the sanding tool while working. Position the extraction as close as possible to the area being sanded.
Once finished, carefully remove any remaining dust before refitting the LED module.
Avoid blowing debris further into the headlight.
6. Refit the Module and Test the DRL
Once the light-guide ends are clean:
- Clean the working area.
- Refit the DRL module.
- Reconnect the electrical connector.
- Switch the DRL on.
- Compare the colour and brightness with the opposite headlight.
If burnt acrylic was causing the problem, cleaning the ends should allow the white LED light to pass into the guides correctly again.
When Should the LED Module Be Replaced?
The module should be replaced if the acrylic light guides are clear but the LED output is weak, discoloured or faulty.
If both the module and light guides show signs of heat damage, repair the light guides and replace the module.
We supply a replacement module for the H1BB-13D278-AC / 208479-00 / ST5872H / L90156368 type used on a number of Ford headlights.
View the Replacement Ford H1BB-13D278-AC LED DRL Headlight Module
Always compare the part number on the original module before ordering.
When Can't the Light Guide Be Repaired?
This method is intended for light guides where the heat damage is concentrated on the exposed end.
Sanding may not be suitable if the acrylic has:
- Melted significantly
- Become badly misshapen
- Cracked
- Burnt deeply into the guide
- Suffered damage further inside the headlight
In these cases, replacement of the headlight may be necessary.
Quick Diagnosis
| What You Find | What to Do |
|---|---|
| Burnt light guides, LED module working | Clean/sand the light guides and retest |
| Clear light guides, faulty LED module | Replace the DRL module |
| Burnt light guides and damaged module | Repair the light guides and replace the module |
| Light guide badly melted or damaged | Headlight replacement may be required |
| No visible damage | Further electrical diagnosis required |
Important
Take your time when sanding the light guides.
You only need to remove the burnt surface. Removing too much material could affect how efficiently the LED couples with the light guide.
The biggest risk during this repair is allowing sanding dust to enter the headlight, so good dust extraction is essential.
Before buying a complete headlight or replacing the LED module, remove the module and inspect the ends of the light guides first. A small amount of burnt acrylic can be enough to turn an otherwise bright white DRL yellow or dull.