I got a weird problem going on with a 2000 Expedition. It throws a code P0781, O/D light flashing, but shifts normal most of the time thru all 4 gears & TC locks up at 100% even with the O/D light flashing. When it acts up shifting wise it skips 2nd gear. Checked wireing from PCM to solenoid pack, everthing checks out ok. Has power to solenoid pack also. Dropped pan and replaced solenoid pack with OEM Ford, no chunkys in pan, fluid is mint!! Took for test drive and after about 1/8 mile O/D light came on but shifted fine thru all gears. Then after about a dozen stop & go it started to skip 2nd gear again?? Again at most times it shifts thru all 4 gears perfect with no problems!! Was wondering if anyone has any ideas?? It makes no sense that works perfect even with O/D light flashing.

 

Is P0781 the code that is coming from the OD light flashing? The OD light itself is flashing a code too. count the flashes, noting any skips.

 

The P0781 code is from the computer, memory codes. If you clear the codes & take for a ride sometimes it starts to flash again right away & sometimes not. There again at times it works normal thru all gears, & then no rhyme or reason it starts to skip 2nd gear?? The O/D light on the shifter just sits & flashes at a steady rate & as soon as you pull over & cycle the key off it starts the proceedure over again. Hope this helps!!

 

Not sure if it makes a difference which transmission/engine you have, but the P0781 is saying "Engnine RPM drop not detected when the 1-2 shift was commanded by the PCM".
Since you have already changed the solenoid pack, my SWAG would be you have a problem in one of the wires between the PCM and the solenoid pack.
On your transmission can you manually select 1 and 2? If so, you might try manually shifting from 1 to 2 and then drive and see if you get any different results. (It might just be that the PCM is still controlling the 1-2 shift even though you 'manually' shift it with the TRS.)

 

My scanner tell me that it is a 1-2 gear shift malfunction..try this from a dead stop pull out and when the vehicle shifts gears manually pull it down in to second gear and see if it downshifts.there is a shift diode that goes bad in the trans and it will completly skip second.

 

When the trans is working correct, you can manually upshift, (1-2, 2-3 3-4) and it will shift perfect while holding throttle steady. When it is acting up, shifting manually it misses 2nd gear all together and just revs. As soon as you shift to O/D and let off the gas some, it will shift to 3rd & into 4th and you can feel the T/C locking up. Also drove it around with the scanner hooked up & it shows every gear as it shifts thru. The only thing I havn't done is a resistance test on the PRNDL switch to see if that is working properly. I would almost assume that it is cause the readings from the scanner shows the proper gear selection. I did do a resistance check on all 6 wires from PCM to solenoid pack and they check out. It is also getting power to term 12 & 1 on the trans. This thing is driving me CRAZY!! Not convinced yet that it is a major mechanical failure because it works so good most of the time. Hope this info may help. THNX!!

 

The diode that you are talking about, is that the mechanical diode in the one way clutch or a electrical diode in the solenoid pack? Did replace the solenoid pack to no avail. I did stop up at the local Ford dealer & talked to the tech that fixs trans & he showed me article #01-13-5 that talks about the junk one way clutch assm used between 7/27/2000 & 3/23/2001 (I guess they decided to try something but found out trying to save a few pennies didnt work out so good??). This has a production date of 5/2000. Before & after these dates they used the good ones. When I get the truck back on Tuesday, I will try the manual downshift and see what happens. THNX!!

 

glhjr0001,
check your battery post connections. I had a loose terminal post inside a battery, everytime I went over a small bump, it disconnected then reconnected the power, causing the computer to reset, the transmission to down shift and the OD light to flash. It took awhile to figure out and the problem was gone after the battery replacement.

 

It is the mechanical diode in the one way clutch,As mentioned ,try the manual downshift and see what happens,chances are your rig is skipping second altogether.

 

I'll do the manual shift & some more checking on Tues and post an update at that time. Thanks for the info everybody. I know we will figure it out one way or the other!! I am kinda thinking about the OWC problem being it, but not 100% sure yet at this point?? I will for sure test drive it little more on Tues & also might drop the valve body and check the valves & springs before pulling the trans.

Did have the battery totally disconected when we checked the wireing from the PCM to trans, cleaned them up & rehooked when done. Thanks again!!

 

Well, I took it for a test drive today and tried the manual shift up & down. It did not act up but it did make the O/D off light come on as soon as I shifted trans to 2nd gear manually but didnot slip as sometimes it does. The shift to 3rd worked & felt it shift to O/D great. Also as driving I was able to activate & deactivate O/D flawlessly even with light flashing?? I started to manually downshift thru the gears with solid engagement all the way down to 1st gear. I pulled over and turned off key, restarted with O/d light off, then proceded to start out in O/D under light acceleration & when it shifted to 2nd gear it did not trigger light. Shifted all the way to O/D again with no problems. Pulled over again and tried it a little more agressive throttle and this time when it shifted to 2nd again, light came on & started to flash but no slip, 3rd & 4th were perfect also. Went back and shut truck off, hooked up scanner, check codes & found P0781 in memory codes. Cleared code and took for test drive watching the shift solenoids & CCS. They all seemed to coincide with the proper sequence throughout the drive. Put about 5 miles of in town driveing & no O/D light came on during this time?? Started to head for the freeway, hopped on and drove about 5 miles to next exit, got off & headed back to shop with no light comeing on, shifting perfect thru all gears, O/D on & off perfect. Put truck up on hoist, dropped fluid, dropped valve body. Again, no metal in pan or burnt fluid. Took valve body apart & everything looked good(valves & springs)?? Decided to do a complete trans flush with the BG machine. Completed service & took for the same road cruise with the same shifting results just before the fluid change?? Dont know what to think?? The truck did not once rev up when it shifted to 2nd as it did last time I drove it(last week). Im haveing a hard time beleiveing anything mechanicly going wrong here unless Im not seeing something. Anybody here have anymore ideas? Owner is going to let me know if there are any improvements in the next couple of days, but at this point Im stumped. I did have Ford check the ID tag and it should be the trans with the better OWC assembly, but not 100% positive unless trans gets tore down to actually see. Thanks for the ideas, and any other help that may come!!

 

Just got a call from customer about her truck. Seems as of today not a single problem with the trans. Says shifts great, no O/D light flashing as of yet!! Not sure of the fix, but maybe by dropping valve body and checking it out may of jared something loose or by doing a total system flush with the BG machine helped clean everything?? Not sure what to think here, but all seems well. Will update this post if anything changes. Thanks for reading this post. The info is GREAT and so is this site!! Thanks again!!