1. Attachments are working again! Check out this thread for more details and to report any other bugs.

MG1 or ICE problem?

Discussion in 'Generation 1 Prius Discussion' started by WHCSC, Aug 23, 2017.

  1. WHCSC

    WHCSC Member

    Joined:
    Apr 18, 2012
    276
    63
    0
    Location:
    Omaha, NE
    Vehicle:
    2003 Prius
    Model:
    N/A
    I got the P3120 code and have been trying to diagnose the problem. I have ruled out the A/C already. My search of this forum turned up the following. I don't want it to get lost on here so I'm starting my own thread. If that's not OK, I can delete. Just looking for some help.

    In this thread, though, the OP has codes that specifically indicate a problem with MG1, which is reportedly unable to turn. That's a whole other kettle of fish. MG1 is what spins the ICE to start it, so MG1 being unable to spin would certainly lead to a no-start.

    I would troubleshoot this into two cases:
    1. Is it really true that MG1 can't turn? Easy test: steer all the way to the right, take a few screws out of the right-hand engine under cover and drop that end of the cover enough to see the engine crankshaft pulley. Try to turn it. It's a low friction engine; mine is easily turned barehanded. With the wheels on the ground and not moving, it won't be possible to turn the crankshaft if MG1 won't turn. Or, jack up the right front wheel, pull the shifter out of park, and try to turn the wheel that's off the ground. If it won't turn (or trying to turn it also moves the ICE crankshaft), MG1 is stuck. If you can turn the wheel and the ICE crankshaft doesn't move, MG1 isn't really stuck. If MG1 isn't stuck but you still can't turn the crankshaft by hand, there's really an ICE problem.
    2. Or, if the above tests show that MG1 and the ICE can be turned freely, then the troubleshooting turns to why the ECU thinks MG1 is locked if it isn't, and that might end up being more of an electrical treasure hunt involving the MG1 resolver, ICE crank position sensor, associated wiring, etc.
    So the first step in distiguishing those two cases is to go out to the car and try to spin some stuff. Doesn't cost much, and then we'll know more.

    -Chap

    I'm having this issue now and tried the above tests. I jacked up the front (both tires off) with car in park and could not budge the crankshaft pulley even with the belt loose and using a big wrench. And then I did the second test by jacking up just the front right and spun the tire. The crank pulley spun. My question is, what does this tell me? Is my problem with MG1 or the ICE?
     
    #1 WHCSC, Aug 23, 2017
  2. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,309
    15,098
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    What would be your own conclusion from the evidence before you?

    -Chap
     
    #2 ChapmanF, Aug 23, 2017
  3. WHCSC

    WHCSC Member

    Joined:
    Apr 18, 2012
    276
    63
    0
    Location:
    Omaha, NE
    Vehicle:
    2003 Prius
    Model:
    N/A
    My uneducated guess would be that MG1 is stuck
     
    #3 WHCSC, Aug 23, 2017
  4. WHCSC

    WHCSC Member

    Joined:
    Apr 18, 2012
    276
    63
    0
    Location:
    Omaha, NE
    Vehicle:
    2003 Prius
    Model:
    N/A
    Thanks for the help
     
    #4 WHCSC, Aug 24, 2017
  5. Brian in Tucson

    Brian in Tucson Active Member

    Joined:
    Oct 15, 2016
    981
    453
    0
    Location:
    Tucson AZ
    Vehicle:
    2003 Prius
    Model:
    N/A
    Rather than replacing the whole transaxle, why not just replace the MG-1? Or find someone who could replace the transaxle for you. One that's not a dealer. Here's a decent deal on a transaxle, 2001-2003 Toyota Prius Transmission/Transaxle AT; (CVT)-1498400 I would look on Craigslist for someone who does mechanical work at home. Here in Tucson, there are some fairly wonderful Mexican mechanics who charge reasonable prices.
     
    #5 Brian in Tucson, Aug 27, 2017
  6. 05PreeUs

    05PreeUs Senior Member

    Joined:
    Oct 1, 2016
    1,097
    563
    0
    Location:
    MSP
    Vehicle:
    2005 Prius
    Model:
    N/A
    Re-reading the OP's topic, it appears this is a Gen1 and not a Gen2. From what I recall, the transaxles are not identical, but I think the theory of operation is, so the diagnostic conclusion may not change, but the repair path might be that the only option is a replacement transaxle.
     
    #6 05PreeUs, Aug 27, 2017
  7. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,309
    15,098
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Art's Automotive did an illustrated article about replacing a transaxle half on a Gen 1. The MG1 and MG2 halves are offered separately through Toyota (or were, at the time of his article).

    The drawback he ran into of doing it that way was that any time you separate the halves and replace one, all the bearing preloads have to be set, and those are set with shims of selected thicknesses. You don't know what thicknesses to order until you complete all the rest of the work and get your test measurements, and then you order the shims, which are stocked in Japan, and wait for them to come in before you can finish the job.

    The conclusion of his article was that he wasn't going to do any other transaxle half replacements, just intact transaxle swaps, in his shop, because he couldn't afford a bay tied up with an uncompleted car for as long as it takes to wait on those shims.

    The economics might be a little different for DIY, but the delay would still be a pain.

    -Chap
     
    #7 ChapmanF, Aug 27, 2017
  8. WHCSC

    WHCSC Member

    Joined:
    Apr 18, 2012
    276
    63
    0
    Location:
    Omaha, NE
    Vehicle:
    2003 Prius
    Model:
    N/A
    Pretty crappy deal all around. I'm weighing my options, none of which are good.
     
    #8 WHCSC, Aug 27, 2017
  9. WHCSC

    WHCSC Member

    Joined:
    Apr 18, 2012
    276
    63
    0
    Location:
    Omaha, NE
    Vehicle:
    2003 Prius
    Model:
    N/A
    I thought this would take someone familiar with the Prius?
     
    #9 WHCSC, Aug 27, 2017
  10. Brian in Tucson

    Brian in Tucson Active Member

    Joined:
    Oct 15, 2016
    981
    453
    0
    Location:
    Tucson AZ
    Vehicle:
    2003 Prius
    Model:
    N/A
    If you've got the manual, a good independent mechanic could probably figure it out. Replacing the transaxle isn't rocket science, just a matter of unbolting and unplugging and then bolting back up and plugging in. A lot of little jobs to get the big job done.
     
    #10 Brian in Tucson, Aug 27, 2017
    WHCSC likes this.
(You must log in or sign up to post here.)