Second VSS replacement failed

[Billme]

I’m flabbergasted since doing all this work coming down to two mini fuses that both happened to supply main and backup power to the PCM and GEM.. No5 under the hood, and No13 under the dash..
( I have since corrected this misstatement, it’s No 5 under the dash, and 23 under the hood, sorry)
I guess one could say if you start seeing ghost GEM controlled codes, and especially a PO 500 code that doesn’t trip the engine light, you need to look into what’s feeding power to the computer s.. Needless to say they are finicky without pure uninterrupted power..
What is most surprising is how much this effected other controls without any sign of a code.. The only thing I first noticed was gas mileage, then later how the Torque converter was not releasing during quicker stops..
So what was the PCM doing all this time? I’m guessing it went into some kind of mode using averages, because it was pretty close to real time actual control and hard to notice since no engine light was visible..
The difference is very noticeable now, more low end torque, I barely have to touch the petal to get it to move now, and the shifting is much smoother although now, sometimes when I punch it slightly more, it bumps.. I hope it is the computer still learning..Even though I haven’t checked gas mileage yet, I can tell it’s going to be back to normal..
Got to get some heat in the cab now.. I have put it off as long as I can hehe

 

[jr1under]

I'm seeing #5 under the hood as (20A)Trailer Tow Backup/Park Lamps and #13 under the dash as (20A)Stop Lamp Switch(Lamps), Turn/Hazard Flasher, Speed Control Module. Same in 1999 and 2001 Owner's Manual. Are those the fuses you're talking about? If they are, then I've lost the plot again.

 

[Billme]

I'm seeing #5 under the hood as (20A)Trailer Tow Backup/Park Lamps and #13 under the dash as (20A)Stop Lamp Switch(Lamps), Turn/Hazard Flasher, Speed Control Module. Same in 1999 and 2001 Owner's Manual. Are those the fuses you're talking about? If they are, then I've lost the plot again.

I’m sorry it was No. 5 under the dash, which was the keep alive circuit to the PCM was the main culprit.. I haven’t decided yet why I said no. 13 but it was in the speed control circuit..
owner's manual labels, which don't mention the keep-alive function for interior #5 (the manual often simplifies descriptions). But in the actual wiring and diagnostic contex, it’s there ..
I would have never known that without Grok mentioning it.. Pretty cool..
I’m old and not a professional mechanic, but I know it fixed a very weird problem hehe
Ok I just remembered looking over the Book I changed out No 23 under the hood.. So now, it all makes sense..

 

[Billme]

I finally got the Expedition fixed, had the transmission overhauled.. They forgot to replace my rear seal on the engine, so they took it out and done that.. Drove it for a couple days and the torque converter seal blew.. They redone the whole thing again.. They even put a new TC in.. They paid for the tow too.. No charge.. These guys were awesome.. They also fixed the PO500 thank goodness, it was the sensor harness on the rear differential.. So we now know for sure how this setup interacts with the VSS on the transmission via the ABS control then the GEM, and on to the PCM..
They loved the Expedition..
On to the next problem, changing out the heater core.. I’m going to delay that again till fall, and just enjoy this thing for a while..

 

[jr1under]

They also fixed the PO500 thank goodness, it was the sensor harness on the rear differential.

Wow, respect to the shop for figuring that out. Out of curiosity, how did they figure it out? Was it something they already knew, was there a way to logically trace it back to the harness, ...?

 

[Billme]

Wow, respect to the shop for figuring that out. Out of curiosity, how did they figure it out? Was it something they already knew, was there a way to logically trace it back to the harness, ...?

Using logic.. Based on the location with 300 thousand miles. That wire on the body connected to that bouncing differential ..Grok even suggested it one time.. My head was stuck on components such as the GEM.. I wouldn’t have thought a bad wire would effect the system like that..
They also have a scope to check the square wave signal..
So far, nothing has showed up again.. Have my fingers crossed..
Best thing is my city mileage average can up from 15 to 17.4 mpg, so I can’t wait for a longer trip to check highway mileage..
This whole journey has been fun really, I’ve learned a lot making a silk purse out of sows ear lol..