Error Code P0303 After Oil Change

Discussion in 'Prius v Care, Maintenance and Troubleshooting' started by Chris Papaya, Sep 23, 2025 at 9:45 PM.

  1. Chris Papaya

    Chris Papaya Member

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    Hi there, quick question:

    I just changed my oil at 210,000 miles with 0W-20 full synthetic. Unfortunately I didn't have the correct oil wrench so I had to leave the filter on. (I'll change it sometime soon because I bought one since). I overfilled the oil and simply put the whole 5 quarts.

    However, after I did the oil change, now when I start the car and the ICE kicks on, the engine knocks and rattles a lot. I checked the error code and got error P0303 which shows misfire in cylinder 3.

    I just wanted you guys' opinion? Is it ok to drive the car until this weekend and then I can change the ignition coils?

    Thanks.
     
    #1 Chris Papaya, Sep 23, 2025 at 9:45 PM
  2. rjparker

    rjparker Tu Humilde Sirviente

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    It is possible the 3/4 to 1 quart oil overfill forced liquid oil through the pcv system into the intake manifold.

    Don't waste money and time on ignition coils or plugs before you check out the most common issues.

    1. Does it continue to shake and rattle after the initial start and warmup? Or does it run pretty good?

    2. Is this the very first time for a rough rattling start?

    3. Does it idle poorly and try to stall? Obviously with the engine running.
     
    #2 rjparker, Sep 23, 2025 at 10:38 PM
  3. Chris Papaya

    Chris Papaya Member

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    III

    1A---From a cold start, when the ICE kicks on it rattles and shakes for about 5-10 seconds but then after that it drives fine for my 50 minute drive to and from work.

    2A---Yes this is the first time it started rattling like this, right after the oil change.

    3A---No it does not idle poorly. It idles fine and drives fine all the way home. Only on a cold start where the car sits for a few hours and cools down does it do the rattling thing.
     
    #3 Chris Papaya, Sep 23, 2025 at 11:36 PM
  4. BiomedO1

    BiomedO1 Senior Member

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    So why do you think there's a problem with coils or plugs, when it only does it on cold start-ups????
    Check and mark ICE coolant level, see if it slowly goes down.....

    Good Luck.........
     
    #4 BiomedO1, Sep 24, 2025 at 12:25 AM
    Last edited: Sep 24, 2025 at 12:33 AM
  5. rjparker

    rjparker Tu Humilde Sirviente

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    You certainly have misfires but not coil, plug or injector based. Not when it clears quickly and runs fine. In fact you may go days or weeks before it repeats which often fools mechanics into thinking the $500 - $1000 worth of replacements actually did something.

    Answers 1 and 2 point to an early onset small head gasket leak. Borescope inspection is the only definitive test at this point.

    Answer 3 suggest it's not an egr valve stuck open and certainly not a clogged egr cooler causing misfires. But a block egr flow test can prove it.

    Car Care Nut HG Borescope at 660s


    Excellent Borescope Footage at 6:50
    Honda Misfires on Coldstart Only


    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.
     
    #5 rjparker, Sep 24, 2025 at 2:09 AM
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