O/D Light Flashing Only Goes into 1st & Reverse

[New2PSD]

I've been looking at purchasing a PSD for a few months now and I've found one that I like.

Although I'm new to PSD's I've worked on cars for many years and recently got into diesels so I do have some general knowledge.

The truck is a '99 F350 with 265k miles and 15k miles on a rebuilt transmission.

The truck will drive normally for awhile and then the overdrive light starts flashing and will only go into first gear or reverse.

The transmission seems to be protecting itself but I'm not sure why.

I suspected the Vehicle Speed Sensor but it seems that a bad VSS will cause a harsh shift through all of the gears.

Any ideas what else it could be?

Also, what are the odds that the transmission needs to be rebuilt?

I'm guessing it's a sensor or relay of some sort because the trans is able to function normally for a little while.

Thanks!

[Dietoremain]

sounds like a sensor issue... i know some trannys have a solenoid problem i think? i wish i knew more about these things heres a bump for ya.

[New2PSD]

That's what I was hoping for but after doing a bit of searching it seems quite possible that it needs a full rebuild.

[HOUTX01X]

take it to a shop and have them pull the codes. whats your fluid condition. when mine was going out it would be normal for a few miles then od light would blink. long story short..ended up getting one built because the other was toast. they arent cheap $$$$$$$$$$$

[dhanna6powerstroke]

Check the PRNDL switch on the side of the trans. My 95 did the same thing and when I removed that switch, it was cracked all along the back side. Moisture was getting in it and shorting it out. Might get lucky and that switch is less than $100

[New2PSD]

Thanks, I'll take a look at the PRNDL switch.

[dereku]

its called the MLPS I believe, so if you need to order one you know what to call it.

[dhanna6powerstroke]

Originally Posted by dereku

its called the MLPS I believe, so if you need to order one you know what to call it.

Thanks I couldn't remember the exact name.

[Trackspeeder]

Originally Posted by dereku

its called the MLPS I believe, so if you need to order one you know what to call it.

It can be found under this name too. Transmission Range Sensor.(TRS)

Most parts stores still call it a neutral safety switch.

[New2PSD]

Thanks for the tip but no such luck.

I'm going to drop the pan, check for damage, new fluid, see what happens, pull the codes.

Maybe not in that order, probably just be wasting my money on fluid, maybe I'll tow it over and get the codes first.

I think if I'm real lucky it's a solenoid pack which should give me an SS2 or SSB code.

The dipstick smells strange, not burnt but not like ATF should. Kind of like butter. That's not reassuring.