Help...I need some advice with no start issue!

Discussion in 'Gen 2 Prius Main Forum' started by StephenJ, Aug 22, 2025 at 3:51 PM.

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  1. StephenJ

    StephenJ Member

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    2009 Prius
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    Four Touring
    Let me explain it with a bit more detail and see if you have any more thoughts about it. So with the car on, in park, the hybrid display showing only 2 bars, the engine kicks on automatically as it should with only two bars, the display shows the charging arrows from engine to elec motor to battery like it's charging, engine is running terrible, very rough.....I give it just a little gas and the charging arrows go away (even though it still only shows 2 bars) and the engine smooths out real nice and feels normal.....but it's showing that it's no longer charging the HB even though it's still only showing 2 bars. Also, when it was idling and running real rough and showing that it was charging, I let it run like that for about 5 minutes and the display never moved from 2 bars. That said, I think the hybrid computer might be flaking out and I believe that could just be sending bad info to the display. I might just replace the hybrid computer to see if it changes some of this displayed data.

    What I read about the p1121 coolant valve code was that the coolant valve and throttle body are on the same circuit and if the valve goes bad in a certain way, it can affect the throttle body. BUT, maybe that's bad information....either way, since giving it a little gas smooths it out I don't think that's the issue. The reason I thought it was charging related is because it stops charging as soon as I give it just a little gas and the engine completely smooths out, let off the gas and it instantly gets violently rough.
     
    #41 StephenJ, Aug 27, 2025 at 2:35 PM
  2. pasadena_commut

    pasadena_commut Senior Member

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    The OP's car has a new 12V, which means it is running now with the default engine settings. If anything is incompatible with that, like a dirty MAF or throttle body, iffy plugs or injectors, or a really dirty air filter, it will run poorly. It might have run just fine before all this with the same problems because they accrued over a long time and the car slowly adjusted its settings to compensate. But by changing the battery all those compensating settings went away all at once and the car now needs to adjust to them again. That could take, I don't recall exactly, 100 miles or 200 miles? That this is happening does tell the OP that something is off in and around the ICE, but it doesn't indicate specifically what. Since stepping on the gas makes it run smooth that does suggest the throttle body, but if the OP is going to clean that, it would be silly not to check the air filter and clean the MAF at the same time.
     
    #42 pasadena_commut, Aug 27, 2025 at 3:21 PM
  3. StephenJ

    StephenJ Member

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    Four Touring
    Yes, I tapped on the hybrid computer and it started making ready again. The only
    The tb, maf and filter are all clean and the coils and plugs have been replaced with OEM replacements. It was running bad prior to the new battery, but the 12v seamed weak so I thought it might have been the cause. I'm still puzzled about the display shows the hybrid battery getting charged at idle, while running bad, but as soon as I give it gas and the engine smooths out it stops charging (or so the display says).
     
    #43 StephenJ, Aug 27, 2025 at 4:04 PM
  4. ChapmanF

    ChapmanF Senior Member

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    That's the thing: when the car's standing still and charging, it's not idling. The engine is doing about the same RPM as at idle, but with a larger throttle opening and more load on it (the power going into the battery). You can hear the difference in the exhaust note between 'idling' and 'charging at idle RPM',

    An engine that runs smoothly at idle but roughly when charging at idle RPM, because of the extra load, is a pretty familiar story around here.

    If you're concerned about the battery charge not increasing as fast as you expect, a scan tool that can show you live data like the charging current and the actual % state of charge gives you more to base your observations on than just the coarse bars on the dash display.

    If the engine is running badly, it may well be unable to produce the same charging current at idle RPM that it could if running well.
     
    #44 ChapmanF, Aug 27, 2025 at 5:05 PM
  5. Tombukt2

    Tombukt2 Senior Member

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    He got it running now step on the gas holding the brake and drive let it charge up . After work on 3190 plugs . Look at coil extrn
     
    #45 Tombukt2, Aug 27, 2025 at 5:47 PM
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