Well guys I've googled until I'm blue in the face, and if I have to sift through one more "My O/D light is blinking." threads I'm going to go insane. Hopefully one of you have seen this issue or can point me to a thread where it's addressed.

I have a 2000 F350 7.3 4x4 SRW CC with several issues but right now I'd like to address the one plaguing my transmission. If I crank the truck and take off it will not shift out of first gear, well it might but it'll take a while, be at high rpms, and a hard shift, throwing the 1-2 shift error code. Now if I disable O/D with the button on the shifter and take off it shifts through all gears fine. I can drive it normally and if I hit the highway, when I'm up to speed I can enable O/D, it shifts into O/D and I can keep on trucking. When I stop I disable O/D and take off normally again. After about 10 minutes of driving and several start/stops even with O/D disabled it will eventually throw the 1-2 shift error code and give me a harder shift into 2nd and I guess enters its limp mode but is still drivable. This appears to be the only code dealing with the transmission.

Due to the fact that it shifts fine with O/D disabled, doesn't skip any gears, and I can manually shift it through 1-2-D I'm guessing it's not the mechanical diode I've heard so much about but an electrical issue. Before I bought this truck it had been abused, at one point the front driveshaft came loose and ripped the wiring harness going to the TRS in half. They soldered it back together but it still looks a little rough. I figure this is a good place to start. Can someone tell me what readings I should get at the TRS? Sensor side and plug side. I have the AE enhanced ford bundle and a good DVM. If the TRS can't cause an issue like this where do I go from here, shift solenoid? Any help is greatly appreciated!

TLDR Version
2000 F350 7.3 4x4 SRW CC
Won't shift out of first with O/D enabled.
Shifts fine with O/D disabled.
Can manually shift through all gears.
Eventually throws 1-2 shift error code.
TRS/TRS Harness has been damaged in the past.
Appears to be an electrial issue with the transmission.
Can the TRS cause an issue like this?
How do I test the TRS/Harness?
If not the TRS what could it be, shift solenoid?

 

I can point you to hundreds of threads where the OD light is flashing. That's not the right search term and won't help you solve the problem.

That's a unique problem. I'm going to have to think about that one. When accelerating having the OD off turns on the coast clutch. The coast clutch will supplement the overdrive one way clutch, which should make no difference at all to the 1-2 shift. The problem with the 1-2 is probably not a mechanical diode problem since no mechanical diodes were installed in any 2000 model trucks. Now if someone installed a 2001 trans at some time, it might be the problem. Except that having the OD turned off should make no difference, it should still have shifting problems.

I suppose it could be electrical, but I don't understand how. What's different electrically with the OD on or off? Nothing except the light. And if there were an electrical problem there should be a code for an electrical fault.

You can test the TRS wiring by checking the continuity of each wire from the connector to the PCM. Also check each wire for shorts to power and shorts to ground. You won't find a problem here, because the TRS can't cause this problem.

It isn't a shift solenoid, either. The shift solenoids have no idea if you have OD on or OD off. They just switch on and off according to the PCM's commands.

This one is a real stumper. Congratulations!

 

Mark, Feel free to correct me, what is below is me thinking out loud.

The initial symtoms, of LATE HARSH shifts leads me to maybe a accumulator problem? Broken spring, or sticking valve? If it does it on every shift (with OD not turned off), Could that be a failing front pump? not enough fluid or pressure?

On a second attempt, if your getting codes, then it is likely electronic.

I guess I would start by dropping the pan, removing the Solenoid Pack, and testing it.

If I remember from my ATSG book. test pin 1 to every pin except pin 6.

One of the pins is for the temp sensor, and it will vary widely on measurement, The others should be in the range of 20k to 30k ohms.

Good luck..

 

But the accumulator doesn't know if the OD is enabled or disabled. Why would it act up with OD enabled, but work with OD disabled? How could it do that?

It isn't the pump, because the only shift problem is the 1-2 with OD enabled. All other shifts are fine.

Why would you think it is electronic? The only code is a 1-2 shift code. Almost every electronic failure will set an electrical circuit code.

 

I'm kinda discounting the OD thing and focusing on normal operation with the OD on. the only non electrical error that i know of is when the pcm detects slip via the input shaft and output shaft sensors. Are there more like that? also he says after awhile with the OD off it goes back to shifting late and hard. The OP doesn't really say that the other shifts are fine with the OD on.

 

*I never searched OD blinking light but if you search 2000 f350 followed by anything dealing with OD, hundreds of blinking light threads appear and digging through them trying to find something similar to my issue has been mind-numbing. I'll test continuity back to the PCM just for peace of mind. Should I try to find a pinout/wiring diagram or trace it back manually? I'll hook AE back up and see if I've picked up any more codes. If I have the time this weekend I’ll drop the pan as well and see what I find. On my way home today after hitting 2nd I'll turn OD back on and check for late/hard shifts going to 3rd but I think it’s only 1-2. Are these input and output shaft sensors something I can get to easily and check? *Some more information that I didn’t think of at the time of posting, while at highway speeds in OD, it never seems to kick back down out of OD, even if I put it to the floor. *It’ll get up to speed eventually but never down shift until I slow way down after taking an exit. *Thanks for the info so far guys, this poor truck has been ragged out but I enjoy working on it.

 

Definitely find a pin-out for the Solenoid pack.

symptom of "while at highway speeds in OD, it never seems to kick back down out of OD, even if I put it to the floor. *It’ll get up to speed eventually but never down shift until I slow way down after taking an exit.' tell me that you only have 4th and 2nd, which means it is in 'limp-mode' to me..

I am heavily leaning toward a failed or failing solenoid pack..

Can you hook up AE and have a passenger read off the gear changes as you drive, noting speed and RPM?

That may give us more of a clue as to what is happening with the trans in normal operation, and OD off..

as far as the sensors go, It is possible to reach the output shaft sensor to change it out, but the input sensor, you may be able to. tough reach though, on top of trans, driver side. if you get the output sensor off, you'll see how the input one is bolted in.. Good luck getting the connectors off, i broke one clip on each one getting them to release. I'm not too worried about them staying on, or sealing up, at least they have one good clip to hold them on.

 

Replace that soldered harness?