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Saw a photo of a dash that had a light that said "Retard on"

I tried to google what this dashboard light means or is used for but really could not find anything. It is in a truck if that matters.

  • Do you know any information specifically about the vehicle? Jan 5, 2022 at 14:58
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    Looking further at the dash, this is a diesel truck (I believe). I think the "retard" it is referring to could be some kind of engine brake. Jan 5, 2022 at 15:00
  • @Pᴀᴜʟsᴛᴇʀ2 sorry I know nothing about the actual vehicle. Just saw the photo and wondered what it meant. Thanks.
    – hellyale
    Jan 5, 2022 at 15:06
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    Just looking at the dash, I'd believe this to be a GM diesel truck . Probably a larger truck (like a 4500 or maybe larger). Not a "big-rig" or semi, but one smaller than that. I've tried to Google it with what I know as well, and haven't found much on it. Jan 5, 2022 at 15:18
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    Lol, i love it! It would be helpful to know if it changes depending on who is in the driver's seat :)
    – Jason K.
    Jan 9, 2022 at 16:30

1 Answer 1


It likely means the retarder is active.

A retarder is a braking device commonly used on big trucks or buses in addition to an engine brake. Typically it's hydraulic, like a torque converter with no other purpose than to waste energy by pumping fluid around. When active, it emits a high-pitched whistling sound, very different from the deep rumble of an (intake) engine brake. It might be integrated into the transmission (sometimes called an "intarder") or separate.

It is typically activated by a lever next to the steering wheel. Because it doesn't make all that much noise, one can accidentally leave it on and try to drive around with a partially braked truck, which is why there's a light to warn you (just like the parking brake warning light).


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