Tranny not shifting

[cudaaa]

Has any one had this problem? The tranny was working fine. I left the dome light on for about 2 weeks so I had to jump start the truck. Finally after getting it started I took it for a drive. It seemed to be stuck in 2nd gear. After parking the truck over night & thinking about it went back out started the truck same problem. So I disconected the batteries for 10-15 min. hooked them back up & the tranny shifts fine. Has any one seen this problem before. Is it signs of the tranny starting to fail or just a fluke. Thanks cudaaa

[chrisk1500]

As I just found out recently.....the trans will not shift properly unless it has over 12v going to the ECM.....

When my alternator went out on me the trans would hunt repeatedly in and out of 3rd and 4th gear at highway speeds unloaded......


Charge up the batteries and you should be good to go...

[Cowracer]

Has any one had this problem? The tranny was working fine. I left the dome light on for about 2 weeks so I had to jump start the truck. Finally after getting it started I took it for a drive. It seemed to be stuck in 2nd gear. After parking the truck over night & thinking about it went back out started the truck same problem. So I disconected the batteries for 10-15 min. hooked them back up & the tranny shifts fine. Has any one seen this problem before. Is it signs of the tranny starting to fail or just a fluke. Thanks cudaaa

I lived through that same problem...

Bad news, it will only get worse.

Good news, its a cheap and easy fix...

Your tranny has two shaft speed sensors. On on the input shaft and one on the output shaft. These are "Hall-Effect" type sensors that pick up teeth on a pulse wheel on the shafts (think crank postition sensor)

After years of use, some metal shavings can build up on the sensors and cause erroneous readings. The computer will thow a WTF code and go into limp mode. Limp mode will lock it into first unless you really crank the revs up (redline or better) and then line pressure will force an extremely hard shift to second. And thats all you will get.

If your speedo dies as well, its output shaft sensor, if not, check the input shaft sensor. All it takes is a wrench to pull one bolt out, and the sensor pop out (they are on the drivers side).

You can try cleaning them, but I wound up replacing both just to be safe. Less than $100 IIRC

Tim

[Robyn]

Hmm
Well it sounds like its not a real tough issue no matter.
I would put a good moderate charge on the batteries over night and probably your issue will go away.
The alternator will be hard pressed to keep up with the batteries stone dead and the line voltage will be marginal.
I had this same thing happen on a 95 gasser Burb.

The kids took off to the casino and lost the alternator, they thought they could make it back so they ran it untill it started to give them fits.
The engine started missing and the tranny started to act up.
I met them about 20 miles out and swapped in a fresh battery as that was all I could do at midnight. The truck ran home fine.

[Clean your ducts in PA]

I am having a very similar problem , but on a 99 astro van with the 4.3 litre. Ive had both sensors replaced. Problem went away for a while then, literally two days before I swas going to sell it, the problems all came back. I was told there is another module that the speed sensors tie into. It converts the impulses into a signal for the speedo, trans, and ABS brakes. I know its not this forums forte', but would any of you be able to shed some light on this? I've ben under the dash pulling things apart looking for this module, with no luck. Trans shop wants $250 just to find the damn thingbut I've already sunk close to $600 into this thing for trans related issues.

note-The computer is still telling me there is a bad speed sensor. I've tried replacing the new one, on the off chance it was bad.

[sailun]

So, if this IS a voltage issue, this may be why my tranny usually will not downshift when I stomp it at highway speeds, if the A/C is on ?

In other words, just when you need it, it won't.

As I mentioned in a previous post, I've learned to turn off the A/C when I need the tranny to downshift on a long hill.