1991 F250. Trans was being funny the last couple times I started it. It wouldn't go into gear until I moved it from drive to reverse a couple of times. Then on my way home the other day, just switched itself into neutral and won't register being in any gear. (I was less than a mile from home thankfully LOL) It's a fairly new trans, fluid seems fine. Can a bad MLPS have caused those symptoms and added up to this total failure?

 

I'm no expert but I think you're on the right track with the MLPS. I would check the linkage as well and just give everything a good visual check.

 

I am an expert, and I know for a fact that there is no way that the MLPS can cause a neutral condition. It's impossible.

While we are going down that rabbit hole, I'll add that there is NOTHING electronic that can cause this. It has to be a mechanical problem.

The next step is to put a pressure gauge in the test port and see if there is line pressure. The test port is on the driver's side of the trans, towards the front, just above the pan. It has a black hex head plug from the factory. The thread is 1/8 NPT.

 

What exactly does the MLPS communicate to the transmission? Obviously I incorrectly assumed it had more control over gear selection than it does.

 

It tells the PCM where you have the shift lever. i.e. park, reverse, neutral, etc. It cannot command the trans into neutral.

When the MLPS indicates park or neutral gear selection, the PCM commands the shift solenoids to the first gear position. That will not shift the transmission to park or neutral. In order to get park or neutral position, the manual valve, which is physically connected to the shift cable, must be in the park or neutral position.

 

The reason we hear about (I've had it happen myself too, what's extra nasty is, it usually bangs violently back into gear when they fail like this too) a range sensor/MLPS acting like it's going into neutral when it fails, is because sometimes when they fail, they can send false info to the trans that's in 1st gear and as Mark explained on the forums, the one way clutch overruns and it feels like neutral. They did this, so that one can't accidentally downshift that low at high speeds and blow things up, (and in the event of failing sensor too) I speculate.
Transgo shift kits have a mod that you can do while installing their kits, that allows the trans to downshift into 1st at any speed! I dunno who in the world would want to install that one haha, and furthermore if one does, and they get a range sensor that fails in this manner, say, going interstate speeds, I'd sure hate to know what would happen!


At a stop, the trans should always have reverse, 4th gear in D position and 2nd gear in both the manual 1 and 2 positions, without power to trans. If the trans is "fairly new" and it's still under warranty, don't touch it and take it back to the trans shop.

I was going to say, make sure your T-case isn't the problem, if you have a 4wd, but you said you do have reverse, so, a bad t-case wont have any gear of course haha.

 

I don't have reverse, no gears at all whatsoever. It is a 4WD also. I haven't had a chance to get under there and check the pressure, was 111 yesterday, 116 today here in southern Oregon, and tomorrow's supposed to be 110+ as well.

 

Here's a good transmission pressure gauge.

https://www.summitracing.com/parts/otc-5610

I used it before I had the C6 in my Bullnose truck rebuilt.

https://www.ford-trucks.com/forums/1...c6-dieing.html

Don't forget:

"He who dies with the most tools wins!"

 

I am in Mid Oregon also , South if Diamond Lake , and it has been too hot here to do much but drink beer . Have to stay hydrated.