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Is my TCU bad? Or is it the Transmission

Posted by FastGS-T, Mar 29, 2010
Automatic Tranny - 4G63 automatic tranny discussions. Sponsored by Import Performance Transmissions

  1. FastGS-T

    FastGS-T Proven Member

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    Arab, Alabama
    I got a 91 AWD Auto car that had been blown up. Owner said he 'got on it' in first and tried to shift up into 2nd but it didnt and it threw a rod.

    He also said that sometimes while just driving it wouldnt shift out correctly, but other times it would be fine and pull hard. He claimed it was the TCU

    Do these cars have normal TCU problems or do I need to get this transmission rebuilt instead?
     
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  2. TFFC

    TFFC Proven Member

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    Chino, California
    The Tcu, normally doesn't have problems, its not like the ecu, where caps leak, ect. You should check the codes on the tcu, sounds like its in limp mode, that will keep the car from shifting!
     
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  3. 8urwrx

    8urwrx Proven Member

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    Elkton, Maryland
    Some TCUs are prone to cap leakage. The one that was in my car before the 5spd swap had a leaking cap which in turn ate up the boards pretty bad. Just open it up and look for any signs of leakage. I have one here that I could snap some pics of to show you what im talking about.
     
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  4. rbwtrans

    rbwtrans Proven Member

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    pensacola, Florida
    Actually, it's quite the opposite. The TCUs fail just as often, for the same reason. Do you really think that Mitsubishi put "better" caps in the TCUs? No, they didn't. I've seen the damage so bad that you could put a finger through the hole in the board. The cap acid damages the board in the shift solenoid and speed sensor circuits and can cause the TCU to short to ground. Try to pull codes from it and then pull it and remove the cover. The caps are in the center of the board, right behind the plugs.
     
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