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One of the rear tail lights of my Mk5 VW Golf blew out recently, triggering a bulb failure warning on the dash.

On inspection it was the bulb itself that was broken, so I have no reason to suspect electrical issues.

I bought some replacement PY21W 12V LED bulbs and installed a pair on the rear tail lights. However, when I turn on the lights the LED lights only turn on for 5 seconds and then turn back off. The incandescent bulbs remain on.

If I turn the headlights off and on again, the LED bulbs come on for another 5 seconds, then turn off again while the other bulbs remain on.

I continue to see the Bulb Failure (solid light) on the dash. I suspect this is to do with the lower current of the bulbs (or some other attribute) being detected as a failed bulb and the power being cut after some time out. Is there some setting I can change somewhere, or do I need to go back to incandescent bulbs?

Here are the bulbs that I purchased.

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  • I don't have time for a full answer right now, but LED brake lights and turn signals need resistors installed with them in some cars so the car thinks is a proper incandescent bulb. These are commonly sold on any site that sells LED bulbs.
    – JPhi1618
    Mar 14, 2018 at 15:28
  • Consider adding more info on the bulbs here instead of linking to the site where you bought them. That link will be dead eventually and not helpful to anyone who sees you question in the future.
    – tir38
    Apr 29, 2018 at 20:19

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There are few issues with this. First was to replace just one side with LED. You will either to replace one side with incandescent bulb or follow through with LED conversion.

If you want to go the LED route, you will need to replace both sides and then alter the coding in the car using something like rosteck vagcom or OBD11 (not sure if supports mk5). Adding resistors will also solve the issue but not as clean solution.

This is because car expects certain voltage / amperage to be drawn by the bulb. If the condition is not met car will throw the bulb out error code. Because LED lights are more efficient they will draw different kind of current than incandescent ones.

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