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I’m building an RV12is and attempted my very first engine start. Fuel pressure is good at ~ 43.5psi and Battery volts are at 13.1 v. I turn the key and it fires right up, but then immediately shuts down with both Lane lights illuminated. Ive made about 9 attempts with different throttle settings and it always shuts down the same way and after the same amount of time.

I just cant get the engine to stay running. All I get is about 2 seconds of it revving up to around 2700 rpm before BOTH Lane A and Lane B lights illuminate. Then the engine quits.

My Garmin display shows “Lane A Caution” and “Lane B Caution”. Ive attached a picture below.

Ive checked every connection that I was required to make via the build manual, and it all matches exactly. I just don’t understand why it can’t continue to run after the initial start. I even tried holding the key to start for extended period, but the engine still shut itself down like all the previous attempts. It just revs up and then right back down. I cant get Garmin to give me any more specific fault other than the generic “Caution” as seen in the picture.

My only thoughts are something related to the "generator swap" that supposed to happen has the engine picks up and drops battery power for generator power. If im misunderstanding that concept then please correct me!

Beyond that, Im absolutely out of ideas on what might be causing this to happen. Please help!!

8950_1_IMG_20211116_065300436_HDR.jpg (You do not have access to download this file.)
  • Re: Lane A and B fault during start (Engine quits))

    by » 9 months ago


    Give it a few more tries.
    My first start took about 10 tries before it remained running.
    Each start, it ran a little longer but eventually stayed running.
    It initially starts on only the B fuel injectors and then switches on the A injectors when the A Gen comes online.
    But the A injectors are still full of air initially.  Game over!  Or at least Time Out!
    Give it another half dozen tries.

    If it will start and run for 2 seconds after releasing the Key, it WILL Run.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


    Thank you said by: Wesley Jordan

  • Re: Lane A and B fault during start (Engine quits))

    by » 9 months ago


    Bill you were right!! Thank you!!

    It took another unsuccessful start this morning followed by a successful fully operational start right after!

    In total it was 11 start attempts for me. No Lane lights at all during or after the engine started (on the successful run). I ran it for around 3 minutes checking various monitoring pages on the EFIS, then id a normal shutdown. I inspected the engine bay and all the connections I could think of without any leaks or burning anywhere. 

    I then did another start and this one started smoother and faster than the one before. Amazing!

    Call it growing pains? Or just a young stubborn engine? But she works!! I'm so relieved!!


  • Re: Lane A and B fault during start (Engine quits))

    by » 9 months ago


    Once you get all the air out of the fuel system of a newly installed engine, you can expect reliable starts.

    Do not expect it to start after one blade, however.
    This is a computer-operated engine.
    The ECU needs to determine where Top Dead Center is before it energizes the injectors and plugs.
    It monitors the timing teeth on the Rotor assembly looking for the missing tooth at TDC.
    Then it counts the timing teeth for one more revolution and if the missing timing tooth arrives again when expected .... Game ON!
    This means you may hear 2 to 4 compressions go by without the slightest hint of it trying to start.

    Also, this engine often hesitates at the first compression.
    The prop makes a quarter turn and then appears to almost come to a stop before continuing.
    Just keep holding the Key ON.

    So a typical start sequence tends to go like this.
    Turn the key and hold it. (No matter what!).
    Prop turns, Hesitates, and continues on.
    Pucka, Pucka, Pucka, Vroooom!

    I have also noticed that the throttle position makes no difference despite the 1/4 throttle recommendation.
    I start at full idle without any issues.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


    Thank you said by: RotaxOwner Admin

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