4r100 falling out of gear - Ford Powerstroke Diesel Forum
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Old 04-19-2010, 01:49 PM
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4r100 falling out of gear

First post here, been on other diesel sites trying to get some info as well.
Well this is what my truck does. OD light will flash when you pull up to a redlight and it feels like the trans looses what gear its in. Once it starts to roll it goes into first and shifts through all the gears fine. This is with the selector in drive. You can put the selecter in first and the trans goes into first and stays there. Well i ran a code scan and got a p0720 code. I know its for the OSS so i replaced that sensor and still getting the same code. So I next i pulled the whole wire harness for the trans looking for breaks or bad wires and ohmed and visually checked and couldn't find any bad wires.
Next i hook my scantool to it and go drive it, in data stream mode the transmission selector switch matches the shifter. As far as in park it says park, drive, it says drive. There is a listing called transmission gear and it says my truck is in 2nd when it should be in 1st. My transmission mechanically feel good. no slipping and shifts 1-2 2-3 3-4 and locks converter in 3 all like it should. When i watch it on the scan tool it says my trans is saying it shifts 2-3 3-4 4-invalid. I don't know understand could make the pcm read this and why i am still getting the p0720 code. Also when the od light is flashing and you shift the truck from drive in park, it will rev up a couple hundred rpms and then back down. Any info would be greatly appreciated.

My trans shifts solid firm and doesn't slip so i'm not convinced yet that its a mechanical problem with the transmission.

Thank you
Tim
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Old 04-20-2010, 06:10 AM
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Any one have any ideas for me? i'll looking for any info
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Old 04-20-2010, 06:22 AM
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I am wondering if maybe you cylinoid pack is starting to go. It is what controlls the trans what gear and when. A stickey cylinoid could cause this and that is what cylinoids do when they start to fail.
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Old 04-20-2010, 06:29 AM
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I understand that, I guess what confuses me is that it shifts through the gears fine. But i guess at that point it has line pressure on it. What does the black box that the linkage cable hooks to do? And i don't understand why i'm still getting a p0720 code after replacing the sensor and I checked the wire harness and there are no bad wires. What else could cause this code?

Last edited by tholt34; 04-20-2010 at 06:38 AM.
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Old 04-20-2010, 04:56 PM
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The symptons you describe about the scanner saying 2nd gear but the trans actually being in 1st gear, that sounds like a bad scanner programming. Mine does that on some GM's.
Put the solenoid pack on the bottom of the list. They hardly ever go bad.
Falls out of gear at stop??? Sounds like low fluid or filter fell out of place.
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Old 04-20-2010, 05:39 PM
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WEll i had the scan tool on my brothers 2001 f-250 and it read correctly. I have everything out right now and i can't find anything wrong with any sticking valves or anything. I still haven't checked line pressure yet, and the filter was in place.
I guess it feels like it goes from should be in first to like in between and it feels like its in a little bit of a bind and when you move it drops back into first and shifts out fine.

If it was line pressure and causing it not to hold a gear, would that still make it flash a p0720 code? What rfi interference? I have heard of alternators causing interference or fuel pump? any ideas on that?

Last edited by tholt34; 04-20-2010 at 07:11 PM.
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Old 04-21-2010, 05:16 AM
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You have the trans out?? and apart??
Have not seen rfi a problem on fords. So you have a speed sensor on the top of the diff??
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Old 04-21-2010, 05:56 AM
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I just have the pan off of it and pulled the valve bodies out.Trans is still in the truck. I've replaced both sensors on top of trans and the vss on the rear chunk. Driving home last night, I ran it pretty hard and it shifted great and never a hiccup. but i still get this p0720 code.
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Old 04-24-2010, 06:27 AM
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Well guys, talked with brian at bts. He thinks my alternator is interferring with the sensors on the tranny. Replaced my alternator and so far no more troubles. He was very helpful on the phone.
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Old 04-24-2010, 06:46 AM
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That is freaking crazy!!!!!!!!!!!
Who in the heck would even think to look there?
Glad to hear.
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