Mild sulfur smell when heat is on

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by indel, Jan 22, 2026 at 3:28 PM.

  1. indel

    indel Member

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    Location:
    Northwest Indiana
    Vehicle:
    2012 Prius
    Model:
    Two
    2012 Prius Two
    144K Miles

    - Engine does not burn any oil (at least it hasn't in the 2500 miles I have driven since I bought the vehicle)
    - No DTCs, pending or otherwise
    - No drivability issues, even in eco mode.

    A couple of times I have noticed mild sulfur like smell when the heat is on. The first time I was driving through rural area surrounded by farms, so I thought may be it was the fertilizer. But yesterday it happened again in the city. When this happens, I do not have any loss of power, no rattling noise and certainly no CEL or any codes in the system.

    I wonder if it could be the cat, or something else. How should I go about diagnosing this intermittent issue?
     
    #1 indel, Jan 22, 2026 at 3:28 PM
  2. PriusCamper

    PriusCamper Senior Member

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    Next time you smell it, pull over and check your exhaust system, as well as figure out if the smell is stronger inside the car or outside the car.

    I mention the exhaust system because back when I was a kid in the 80's my Dad bought a European car on the grey market and shipped it to California and had it equipped with emissions gear to get it road legal and that exhaust system was never quite right and had an overwhelming sulfur smell that never went away until the exhaust system cooled down.
     
    #2 PriusCamper, Jan 22, 2026 at 3:40 PM
    indel likes this.
  3. indel

    indel Member

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    Can you expand a bit upon what you mean by check the exhaust system? A leak from exhaust manifold? Are you suggesting that the smell may be stronger in the engine bay if that's the case?

    One technical question: what proportion of exhaust gases are sent to EGR instead of tail pipe? I don't the mechanics of this but what are the primary leakage points? A gasket between the EGR cooler and the exhaust manifold may be one. Are there others?
     
    #3 indel, Jan 22, 2026 at 3:50 PM
  4. PriusCamper

    PriusCamper Senior Member

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    My point: Is the smell coming from inside the car or outside the car? Until we know that, we can't narrow it down.
     
    #4 PriusCamper, Jan 22, 2026 at 4:08 PM
  5. indel

    indel Member

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    Gotcha.

    When I did some googling, 12V battery was mentioned as one of the potential culprits. I have a brand new 12V (Toyota oem) that I installed last month. I will check the vent tube to make sure it's not loose or something.
     
    #5 indel, Jan 22, 2026 at 4:11 PM
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