2015 Prius V gas motor start up feels like a read ending?

Discussion in 'Prius v Technical Discussion' started by kevinprius416, Oct 25, 2025 at 3:18 PM.

  1. kevinprius416

    kevinprius416 New Member

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    I just picked up a 2015 Prius V with 130k km (80k miles). Car was Toyota dealer serviced till it was traded in early 2025 and then it sat forgotten in a car lot till I bought it early October. Dr Prius reports approx 72% battery capacity and I get as low as 4.6 L/100 (51.3 MPG) but average around 5.4 L/100 on a typical drive (43.6 MPG).

    Since picking it up, I've followed along with the extra maintenance recommended on this board:
    replace water pump (ASIN), thermostat (OE), coolant hoses, clear egr, clean intake egr ports, drain and fill coolant (engine and inverter) and did an ATF drain and fill as well.

    The gas engine does not have any coolant seepage or any signs of the death rattle on cold start

    However, I notice if I'm stopped in traffic or at a light, when the gas engine does decide to kick on (hot or cold), it feels like somebody rear ended me. Now I understand, the gas engine is being started with a rather larger electric motor. I'm used to shaking the entire car in my fun cars on a cold start.

    I've checked the motor mounts and they visually look ok and do not have excessive pry bar movement.

    Is this normal?
     
    #1 kevinprius416, Oct 25, 2025 at 3:18 PM
  2. rjparker

    rjparker Tu Humilde Sirviente

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    You can feel it but it should not feel like it was rear ended assuming your foot is on the brake.

    You did all the expensive things early but did you do the easy throttle body and maf sensor cleans?

    If that does not smooth things out it might be worth checking the egr valve and egr valve to intake gaskets for the real egr issue, eg an egr valve sticking open at low rpms or a vacuum leak on the gaskets after previously tearing it apart.

    Egr flow block test
    Starts at egr block flow test

    At about 10:15 in the video he starts talking about the egr valve letting "air" into the intake manifold. He means exhaust gasses.
     
    #2 rjparker, Oct 25, 2025 at 6:20 PM
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  3. ChapmanF

    ChapmanF Senior Member

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    A rear-end collision usually jolts the car forward.

    There are two rather large electric motors in the transmission. MG2 always turns with the driving wheels, so it isn't free to be used to crank the engine; if you're stopped in traffic or at a light, MG2 is necessarily still.

    When MG1 spins to start the engine, it's effectively using the drive train as a fulcrum. MG1's effort to crank the engine forward is also a force to lurch the car backward (the opposite way from a rear-end collision).

    The car knows this, of course, and since it knows what torque it's going to apply with MG1, it can also calculate the forward torque it should apply with MG2 with the aim to cancel out the backward lurch. It works pretty well, but still you can feel it. One wildcard the electronics can't predict perfectly is just how eagerly the engine will catch. If the car overestimates how hard it'll be to crank, the car might lurch forward a bit (as in a rear-ender).

    The gen 3 has an additional trick to minimize the lurching if you are stopped and in P with your foot off the brake: it will actually apply the brakes itself just before starting the engine (you can hear the faint click-squish, if you listen closely, just before the engine starts). Of course it can't use that trick when the car is moving, and it's redundant if you already have your foot on the brake.

    So, a bit of a perceptible lurch is always involved. I wouldn't call it like being rear-ended myself, but I've been driving Prii for 17 years so I'm kind of used to it. Is this your first?
     
    #3 ChapmanF, Oct 25, 2025 at 6:51 PM
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  4. kevinprius416

    kevinprius416 New Member

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    I did clean the throttle body and maf while I had it out.

    I did check around the EGR for leaks with soapy water after I cleaned it, did not see anything. I have a smoke machine I can do a better test with when time permits... as well as try the CCN blade test. It did feel like this before I cleaned the EGR, my cleaning did not make it better or worse.

    as for the rear ending feeling, it's more of soft rear end feel... like when the car behind you in stop and go rolls into you.... I've actually looked back a few times because I thought somebody rolled into me when the gas engine fired up.

    My apologies, I don't mean a full violent rear ending, more like a car rolling into you from behind in stop and go traffic... a tap with barely any paint transfer type of rear ending. If I'm sitting a light with my foot on the brake, the car jerks a bit when the gas engine starts, no jolting forward.

    This is my first Prius, first hybrid I've owned... I have had a rental Rav4 Hybrid before, I believe it was a 2023 MY.
     
    #4 kevinprius416, Oct 25, 2025 at 8:23 PM
    Last edited by a moderator: Oct 25, 2025 at 8:47 PM
  5. bisco

    bisco cookie crumbler

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    it's a tough call for a prius newbie, could be normal, and you don't want to waste time chasing ghosts.
    if there's any way to find another gen 3 to drive, that might be useful.
     
    #5 bisco, Oct 25, 2025 at 9:09 PM
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