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O/D on/off selector weirdness


fastpakr

fastpakr

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In my '99 3.0 4R44 truck, the overdrive on/off button seems to work in any position except Drive. In P/R/N/2/1, I can use the button to disable overdrive, then shift back into the drive position. From the Drive position itself however, nothing happens when I hit the button (most of the time, of all the times I've tried, maybe two or three of them it's actually worked). Is this possibly a range sensor issue? I'm really not sure what to blame here since the button itself obviously works.
 


fastpakr

fastpakr

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Had a little time to dig into this yesterday after the button stopped working entirely. I assumed it was a chafed wire issue but now I'm more confused than ever.

1) With the switch connector disconnected next to the column, I don't see any continuity across the terminals to the switch when it's pressed or released.

2) I checked the fuse and confirmed 12v to the switch connector on the vehicle side of the harness. My assumption was that I could short those pins briefly to enable or disable overdrive, however there's no response whatsoever when doing so (either in the form of a click, or the O/D off light coming on in the cluster).

Anybody know more about testing this circuit, via a pinpoint troubleshooting sequence or other means?
 

RonD

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Transmission Control Switch is what Ford calls the OD button

Its wire runs to the computer(PCM).
When key is first turned on PCM sest OD on, thats default setting each time PCM boots up
Pressing the OD button tells PCM driver wants to turn off or on OD, depending on current state.
PCM turns on and off OD dash light for that state, button has no physical connection to dash light
Key off then on resets to OD on every time

In 1998 3.0l OD switch gets 12v from fuse #27 in cab fuse box on Purple wire
Then when switch is closed(pushed) it sends that 12v out a Tan wire to pin 29 on PCM
And that 12v toggles the PCM to turn OD off or on

So when button is pushed you should see 12v on both wires, if not replace switch

In 2000 3.0l they used fuse #6 but same wire colors, don't have 1999 diagram
 
fastpakr

fastpakr

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Right, I seem to have two separate issues as far as I can tell. One is not getting continuity across the switch terminals when it's pressed, but the second is that jumping power on the vehicles side of the connector doesn't seem to be toggling the PCM.
 

RonD

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Key would need to be on

And you should see 12v on the purple wire then, and then 12v on tan wire when button is pressed

There would be a connector in steering column to main harness

Pin 29 on PCM in engine bay should be that tan wire and should have continuity with tan wire at switch
I use sewing needles to pierce wires to test
 
fastpakr

fastpakr

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Automatic
2WD / 4WD
4WD
Tire Size
285/75-16
With the key on, I verified that there was 12v at the connector on the steering column that goes to the main harness. I then jumped that connector and the PCM didn't toggle.

Separately, I tested the connector going to the switch with a meter. I see no change in resistance between the two terminals when the button is pressed.
 
Last edited:
fastpakr

fastpakr

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113
Location
Roanoke, VA
Vehicle Year
1999
Make / Model
Ford
Engine Type
V8
Engine Size
5.0
Transmission
Automatic
2WD / 4WD
4WD
Tire Size
285/75-16
Back to square one...

Not sure why jumping the terminals at the connector didn't work, but I found a break in the switch wiring harness and temporarily bypassed it so everything works at the connector (open normally, closed when the button is pushed). The O/D light cycles on or off each time the switch is pressed just as it should - except when in Drive. Any thoughts on this? The range sensor appears to be set correctly at the transmission and it starts perfectly in Park and Neutral.
 
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