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Transmission slipping our of gear when driving

In my 2004 Ford F150 fx4 truck the “transfault” light came on and then while i was driving the transmission slipped out of gear and would not go back in. Even when I stoppd it still has the issue. Will I have to replace the trasmission?

I have no specific knowledge to offer, but there are a number of different things can go wrong with the transmission. You could need something as complicated as a rebuild or as a simple as a repaired wiring short - or anywhere in between.

Have you at least checked the fluid?

For anyone to give advice the first thing that would be needed would be malfunction codes from the computer. Some kinds of transmission codes are routine powertrain codes that can be read with any OBDII reader. Large chain auto parts stores do this for free, and some will “lend” you a code reader to use at home. (You pay for it and they refund the $ when you bring back). Try that and report what comes up.

Other codes need better/different scanning equipment and for that you’ll want to get the truck to a local, independent transmission shop and have them scan it. You can see what they say and also post the codes (the exact codes) here for comment and advice.

we checked the transmission and it was empty so it was filled then we connected one of the OBDll readers and it came up with no codes. then we baked the truckout of the drive to see what happened the light went off but its still slipping. that is why we are puzzled

I doubt that the transmission was “empty” - how much fluid did it take to get it back up to level and what is the total capacity ? (total capacity should be in the maintenance section of your owner’s manual). What kind of fluid did you put in - you need Mercon V. I wouldn’t put anything else in it.

I also just have to ask to make sure that you know how to check the trans fluid - the engine must be hot and running, with the transmission in park (sometimes neutral - also says so in the manual). If you check it without the engine running you might think it is full when it is still quite low. This will contribute to slipping.

While the transmission was lacking fluid and not working how much revving of the engine was done? If you tried to drive it anyway and did a lot of revving while it was slipping then you may have burned up the clutches which is why it is still slipping. In this case you will need a rebuild.

If you happen to get the fluid up to level with the correct fluid and it doesn’t slip, then you may be ok - BUT you apparently have a substantial leak that needs to be taken care of right away.