Drivetrain Overdrive Issue

Discussion in '1994 - 1995 Specific Tech' started by JonezySN95, Jul 8, 2012.

  1. Overdrive button changes nothing when pressed. Tested all the way up to 70 mph. I took apart the switch, cleaned all contacts, and have good continuity through the switch. I tried looking for a schematic but not even my trusty page of diagrams has one that points out the O/D switch so I can trace the prob unless I overlooked it. Any input is appreciated...

    This is the schematic I was looking at but no luck.

  2. See if this helps. It's from the service manual.
    Transmission Control Switch

    The transmission control switch (TCS) is a momentary contact switch located on the floor shift console, next to the gearshift lever (7210). When the switch is pressed, a signal is sent to the powertrain control module (PCM) (12A650) to allow automatic shifts from first through fourth gears or first through third gears only (locking out fourth (O/D) gear). The powertrain control module then energizes the transmission control indicator lamp (TCIL) on the instrument panel to indicate O/D OFF.

    On the AODE application, the TCS signal is sent to a transmission control switch module (TCSM). The TCSM sends the signal locking out fourth (O/D) gear to the PCM and turns on the TCIL to indicate O/D OFF.

    If the OD light is not illuminating it would appear the ECU isn't sending a signal to the TCMS. Here's the wiring for the OD switch and the TCSM.

    The location of the module is behind RH side of I/P
  3. While testing, did the switch show continuity while depressed (it's just a momentary switch as I recall)?

    Does the OD light come on when the button is depressed? If not, check your trans control module. It's behind the glovebox (it's just a little black box a little smaller than a deck of cards). It's what turns off OD (IIRC they didn't have room in the ECU for this so they used a little module to handle it). It should have a label on it with a part number similar to F4ZF-7E453

    Good luck.

    EDIT: Richard posted while I typed. Great post BTW. :nice:
  4. Thanks guys. Sorry it took me so long to reply, I've been pretty busy getting ready for my move. The light does not light up when I push the button. Nothing happens at all, but I do know the switch is good. I have continuity when its pushed and none when released. I'll have to trouble shoot later unfortunately... I've been having running issues and kept getting 172 lean code. Sounds like it was missing real bad and went through almost all the electronic parts trying to solve this. I finally got fed up with it and pulled the top plenum off and my valve covers. What I found makes me put this project behind me until after the move and I go pick up blackverts 410w. I have oil and what appears to be gritty sand in the intake, and I also somehow broke a valve spring seat on the right side and now have big curly metal shavings and tiny flakes all through the head. I'll try to post a pic from my phone.