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94 trans not locking up

Farmer12

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I’ve done searches but not coming up with anything.

94 2500 213k 6.5td. It will lock up once when initially started but if I stop at a stop sign and go it will not again until I shut it off. I am getting a brake on code. Which I’m sure is why it’s not locking but I can’t figure out why. Switch is new, and it doesn’t look like there’s any sort of adjustment on these. Even if I hold the pedal back it doesn’t change anything. Ive checked the trans plug as well. Not sure which way to go. I can’t drive it like this, don’t wanna cook the trans. Any ideas? Appreciate any help.
 

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FRANKENBURBAN
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Are ALL of your brake lights working? 1 side of the brake switch runs to the 3rd brake light if equipped, and if its blown, it can cause all kinds of problems.
 

Farmer12

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Are ALL of your brake lights working? 1 side of the brake switch runs to the 3rd brake light if equipped, and if its blown, it can cause all kinds of problems.
I didn’t even think to check the lights. I knew they weren’t on bc the code says brake on. I will do that.
 

Farmer12

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Anyone else have any ideas? I have no idea which way to go with it. Any google searches that have anything similar ended up being just a bad switch.
 

Will L.

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I would start by unplugging the 3 brake light switches and clear the code just to ensure vibration of driving and intermittent switches.

Test Drive: in daytime; you’ll have no brake lights at all, so just turn on running lights so people behind you see lights and know you are slowing or stopping.

This would 100% eliminate the switch as culprit. In theory the harness could be chaffed and getting contact but less likely. I remember something a out the connector at the trans, but my sleeping in slackin, just woke up self
cant remember yet.

Important to add, if the clutch was staying locked uo and the 37 was there, it would not allow the ttc to unlock and could stall the engine at a stop sign. Like not pushing in the clutch pedal with it in gear at a stop and the engine dying. So if it lockups up and wont unlock doing this test- slipping into neutral at a stop may be required to get back home.
 
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Will L.

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Ok, more awake now. Iirc that code can set from either the switch being “on” when brake is not being applied, or from the trans input and output speed both slowing as if you are stopping and there is no brake signal.
So that may negate my above idea of just unplugging it.

But if it see there is a non working switch- I think it is supposed to not just unlock the tcc to keep from stalling the engine, but should put the trans into limp mode- 2nd gear only- but I may be wrong about limp mode activation.

Anyways, I am sure the open wires (cut wires) anywhere from the brake switch could cause the same code you are getting.
I think you need a scanner on there to watch you are getting signal every time you apply the brakes, and only when you apply the brakes.
 

Farmer12

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Ok, more awake now. Iirc that code can set from either the switch being “on” when brake is not being applied, or from the trans input and output speed both slowing as if you are stopping and there is no brake signal.
So that may negate my above idea of just unplugging it.

But if it see there is a non working switch- I think it is supposed to not just unlock the tcc to keep from stalling the engine, but should put the trans into limp mode- 2nd gear only- but I may be wrong about limp mode activation.

Anyways, I am sure the open wires (cut wires) anywhere from the brake switch could cause the same code you are getting.
I think you need a scanner on there to watch you are getting signal every time you apply the brakes, and only when you apply the brakes.
Pulled the brake sensor and disconnected it, now it works as it should. So it’s def something on that side. I know some new parts are junk but I wouldn’t think a simple switch would be. Had the same prob with the old switch.
 

Will L.

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You mentioned sensor. Do you mean the brake switch under the dash?

If so, how did you test the switch or did you just unplug it, then trans worked ok. Then you bought a new switch and the problem continues?

Need more accurate details when trying to follow or more unusual problems.
 

Farmer12

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You mentioned sensor. Do you mean the brake switch under the dash?

If so, how did you test the switch or did you just unplug it, then trans worked ok. Then you bought a new switch and the problem continues?

Need more accurate details when trying to follow or more unusual problems.
Yeah it autocorrected to sensor not switch. The switch on it under the dash is new, I recently got the truck from a friend and I assume it was doing it when he had it and he prob didn’t know it.

I did just unplug it and drive. The brake light is on now but that’s to be expected.
 

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With the brake switch unplugged you shouldn't have gotten lockup iirc. The brake switch has 2 sides, one that powers the brake lights, so it's normally open until depressed, and the other side supplies a ground to the cruise(if equipped) and to the trans circuit to allow lockup(it was used on 700r4's to ground the tcc circuit so the converter unlocked when you touched the brakes). I wished I had access to an obd1 6.5l manual to look up the diag flow chart for your code.
 

Farmer12

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With the brake switch unplugged you shouldn't have gotten lockup iirc. The brake switch has 2 sides, one that powers the brake lights, so it's normally open until depressed, and the other side supplies a ground to the cruise(if equipped) and to the trans circuit to allow lockup(it was used on 700r4's to ground the tcc circuit so the converter unlocked when you touched the brakes). I wished I had access to an obd1 6.5l manual to look up the diag flow chart for your code.
That’s strange, the cruise even worked. It wouldn’t when the tcc wouldn’t lock. Is it possible the ecm is getting a signal from the other side of the harness making it think the brake is on?
 
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