MFD won't shut off, trying to trace down

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by jtrosario, Jun 6, 2015.

  1. jtrosario

    jtrosario Prius Pioneer

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    When Powering off my 2004 Prius, here's what happens: Press Power button, Power button and Dash display(above the sterring wheel) go off, while the MFD screen stays on(center console) - although temperature is no longer reported on the consumption screen, the consumtion screen is still on, power outlets stay on, and clock is still on. Car refuses to lock driver's door, even with keyfob located outside of car. Car beeps as though still on - I disconnect 12V battery to leave vehicle(and not wear down the 12V). Happened for 3-4 days, went away for a week, and its been back for a week since.

    Traced problem so far to the three cables behind the 6 CD changer/radio unit. If the middle of the three plugs on the back of the radio/CD player is unplugged, the problem goes away, so does my bluetooth audio. I need to be able to use handfree while driving in my state, also haven't figured out what else is gone when that cable is unplugged. Radio, CD Player, and Navigation still work with sound when that same middle cable is unplugged.

    What to do next? 1) Replace 6 CD changer/radio unit, 2) Bring to dealer and pay $$$ to repair - I haven't even been able to find this issue in Prius chat. Could it be the cable itself - can't figure out where it goes next - assume it's at least to a bluetooth receiver somewhere. Could it be the bluetooth receiver that's bad? Or the wiring harness that was unplugged?
     
    #1 jtrosario, Jun 6, 2015
  2. ChapmanF

    ChapmanF Senior Member

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    See what the MFD diagnostic screens tell you. In addition to any errors, the network check screen will show you what other devices it sees connected; you can compare that list with and without the connector you've unplugged. The "vehicle signal check" screen will let you monitor the various vehicle status signals that are fed to the MFD, which might include the ones it uses to decide when to turn off.

    I've got a Gen 1 so I can't help with the details of how you get into the diag screens on Gen 2, but searching the forum should help.

    Before anybody gets too excited, the MFD diagnostic screens are only useful for diagnosing MFD/audio/nav/... problems; they don't offer the function of a scantool for diagnosing the rest of the car. (Everybody who first stumbles on the MFD diag screens gets excited that way, at first....)

    -Chap
     
    #2 ChapmanF, Jun 6, 2015
  3. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. Restore all wiring harness connections.

    2. The MFD receives 12V power from three fuses: 15A ECU-B, 7.5A ECU-IG, and 7.5A ACC. The reason it receives power from three sources is because the MFD behavior varies depending upon whether the car is IG-OFF, ACC-ON, or IG-ON (or READY).

    3. When the car is IG-OFF you expect the MFD to be dark. However some of the unit retains 12V power. For example the circuits associated with the trip odometer and mpg gauge in the MFD need power to maintain their settings. The ECU-B provides power at all times as long as the 12V battery is connected.

    4. The ECU-IG fuse provides power when the car is IG-ON or READY and the ACC fuse provides power when the car is ACC-ON.

    5. My guess is that the ACC relay, which provides power to the ACC fuse, is stuck closed on an intermittent basis. That relay is hiding behind the instrument panel, in the area where the fuse box is located (near where your left knee would be when seated in the driver's seat.)

    6. If you can find the relay while the problem is happening, tap on the relay case with a screwdriver to see if it will disengage. If it does you know the relay is sticking.

    7. If you should find that the relay is not the problem, then the Power Source ECU (which controls the relay) is being flaky and needs to be replaced.

    8. Consult techinfo.toyota.com for help finding the exact location of the ACC relay and the Power Source ECU, wiring diagrams, etc.
     
    #3 Patrick Wong, Jun 6, 2015
  4. jtrosario

    jtrosario Prius Pioneer

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    2014 Prius Plug-in
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    Plug-in Base
    Thank you so much! I was thinking it could be a stuck relay.(Don't know why, I'm not THAT Savvy) It might take me a while to find, but I'm encouraged by your detailed instrucutions here and will try it this morning.

    UPDATE: Tried Tapping ACC relay while on, off and acc mode, then removing while tapping, can even remove the relay and the same items are still on when powered off. I can't get access to the power outlet relay to test, nor the Power ECU - so maybe to the dealer next week. For now, still disconnecting 12V in trunk to power off completely.
     
    #4 jtrosario, Jun 6, 2015
    Last edited: Jun 6, 2015
  5. SFO

    SFO Senior Member

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    Curious if there was any closure to this problem?
     
    #5 SFO, Jan 2, 2022
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