Is my TCU bad? Or is it the Transmission

Posted by FastGS-T, Mar 29, 2010

Please Support Jackson Auto Machine
  1. FastGS-T

    FastGS-T Proven Member

    Joined Oct 20, 2005
    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?

    Log in/Register to remove ads
  2. TFFC

    TFFC Proven Member

    Joined Apr 9, 2005
    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!
    My DSM:
  3. 8urwrx

    8urwrx Proven Member

    Joined Oct 2, 2007
    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.
    My DSM:
  4. rbwtrans

    rbwtrans Proven Member

    Joined Sep 3, 2006
    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.

Share This Page


Log in/Register to remove ads

Support Vendors who Support the DSM Community
Ace Race Parts Advanced Fuel Injection Archer Fabrication Boostin Performance ECM Tuning Extreme Turbo Systems ExtremePSI Feal Suspension Fuel Injector Clinic Jacks Transmissions Jackson Auto Machine JNZ Tuning Magnus Motorsports Miller Import Parts Morrison Fabrication & Design OHM Racing Race Components Inc RockAuto RoadSurge Spultronix Performance STM Tuned Strictly Import Motorsports VR Speed Factory