EGR Cleaning Diagnostic

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by gatorback, Dec 5, 2025 at 12:44 PM.

  1. gatorback

    gatorback New Member

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    I inherited a 2010 Prius with 90K miles and it is now the daily driver. I gave away the Integra, so it is now my only car and I am motivated to prevent disasters / issues.

    As I understand it, the EGR buildup is similar to arteriosclerosis and will seriously damage the engine (overheating). Is there a simple non-invasive diagnostic to determine if a cleaning is needed?

    If one was open up the system to visually inspect, wouldn't it be silly not to clean it? Or is cleaning a significant undertaking? I am trying to get a sense of time / tools / cost to DIY and when I need to do this. Again, the Prius is 90K miles and 15 years old.

    Google indicates:
    "Cleaning the Gen 3 Prius EGR system involves removing the EGR cooler, valve, and pipe, soaking them in powerful cleaners (like brake cleaner, oven cleaner, or fuel system cleaner), scrubbing passages with brushes, rinsing thoroughly (hot water/air compressor helps), and cleaning the intake manifold's EGR ports, swapping parts for a clean set to minimize downtime, and reassembling with new gaskets to prevent clogging and head gasket issues."

    I am wondering if it is sensible to replace the EGR system parts (EGR cooler, valve, and pipe). So as to minimize downtown and ensure a proper clean at year 15+. I don't have a second car and would like to avoid renting a car.
     
    #1 gatorback, Dec 5, 2025 at 12:44 PM
    Last edited: Dec 5, 2025 at 12:53 PM
  2. burebista

    burebista Active Member

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    Take a look here. Basically you need a decent OBD reader and look at EGR airflow. 21-22 kPa is a value for a cleaned EGR.
    But it won't tell you the whole story because it measures total airflow. Unfortunately in intake manifold are 4 small holes and they clog different so next step is to dismantle intake manifold and take a look at those holes.
    Those are two steps which doesn't involve too much work
     
    #2 burebista, Dec 5, 2025 at 1:42 PM
    Brian1954 and gatorback like this.
  3. Brian1954

    Brian1954 Senior Member

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    A clogged EGR will not cause the engine to overheat. It will cause a P0401 trouble code.
     
    #3 Brian1954, Dec 5, 2025 at 4:24 PM
    Last edited: Dec 5, 2025 at 4:32 PM
  4. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Assuming it's never been done previously, the 90k miles would be motivation enough for me.

    It can be done in a weekend. Prior to starting I would make sure you've got all the tools needed, and a decent idea of what's involved. There's strategies that'll make it easier:

    1. If you're not planning on a full coolant drain and fill, consider just draining a couple of quarts (from the radiator drain spigot) into a clean container, and when done just pour it back into the reservoir. This'll reduce coolant spill to near-zero, and no hose clamping/plugging needed.

    2. Remove the cooler lower bracket nut and stud, any convenient time in advance, and leave it off. Also, remove the cooler top bracket bolt, and the the nut and stud going through the valve into block. Lube both and reinstall. This'll make the eventual removal of the valve/cooler combo go much smoother, and negate the need to remove the studs at the rear cooler connection, to exhaust manifold. This in turn will help to retain the gasket there, and to align it during reinstall.

    3. Get the cooler soaking with cleaner first, and check on it hourly, rinsing-and-repeat till clean. Forget about brake cleaner or similar solvents for this. Either soak with concentrated (water) solution with Oxi-Clean, or for more expedience, either Sodium Hydroxide (NaOH, aka "lye") or Potassium Hydroxide (KOH, aka "caustic potash"). The latter is still readily available, commonly used in soap making. Use appropriate caution with the latter two, they're strongly caustic.



    5. See top two links in my signature (on a phone turn it landscape to see signatures). Also, this workflow may help.
     
    #4 Mendel Leisk, Dec 5, 2025 at 8:59 PM
    Last edited: Dec 5, 2025 at 9:14 PM
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