My overdrive light will start flashing on my 98 4.0 ohv. Then it will shift hard from 1st to 2nd. I can pull over and shut my truck off and start it back up and it will stop. I watched a YouTube video where a guy replaced a sensor in the rear end of his truck and it stopped doing it but every parts store I go to tell’s me that sensor is for the speedometer and has nothing to do with shifting. Can anyone please tell me what it could be? Thanks!

 

Welcome to the forum

Assuming Automatic transmission, its a 5R55E model in a 1998 4.0l Ranger

Yes, the 1998 thru 2000 Rangers did use the rear axles ABS sensor via GEM module for speedometer/odometer, cruise and Computer speed signal

If this sensor was intermittent then ABS light on the dash would come on and speedometer signal would also be erratic, and it would cause CEL(check engine light) to come on as well and set a code
Code P050X
P0500 Vehicle Speed Sensor Malfunction
P0501 Vehicle Speed Sensor Range/Performance
P0502 Vehicle Speed Sensor Low Input
P0503 Vehicle Speed Sensor Intermittent/Erratic/High

Since you don't mention the ABS light or the CEL being on I would say the rear axle sensor is NOT the issue, nor the GEM module

Flashing OD OFF light means computer has detected an issue in the electric system of the transmission or the lack of a ratio change(gear change) during operation
It also means the computer set a Transmission Code, these do NOT activate the CEL, only Flash the OD OFF light when they are set
Turning the key off and on doesn't erase the codes, but does reset the computer so it can operate "normally" until it detects the same or another problem

Most OBD2 code readers can't read Transmission codes, P0701 to P0803, look at the list here: https://www.therangerstation.com/tec...II_codes.shtml

Because ALL OBD2 codes are very specific you need the EXACT CODE number to diagnose any issue that sets a code
Some auto parts stores can read transmission codes, and will do it for free, ask FIRST if their reader can see transmission codes, as said most can not

All transmission shops can read transmission codes, but may charge you to do it
WRITE DOWN CODE NUMBERS
need EXACT numbers or don't bother

You can buy a Bluetooth OBD2 reader that CAN read transmission codes for $90 or so, I use BlueDriver and have no complaints
These Bluetooth readers work with any Android smartphone, check Apple iOS numbers
And work on ANY new vehicle sold since 1996, so not a Ranger thing or even a Ford thing, ANY VEHICLE, its the law

The transmission code(s) can indicate what system is acting up, its not simple with automatics, there are several interdependent systems that are like a "chain", so the broken link is not always as straight forward to see from a code number, but it is a starting point you should take advantage of

 

+^^^
Welcome to the herd!
Some very knowledgable+friendly folk in these forums, especially RonD.
Yep, you seriously need an OBD2 Scanner that will read both StandardSAE+ProprietaryFord data.
I've got the OBDLink# MX+ & EX OBD2 port modules, that work with AndroidPhon+OBDLinkApp & WindowsPC+ForScanApp;
there are less expensive ELM modules available.
Sounds like a blown out 5r55e ValveBody gasket; a rebuilt ValveBody & new BondedGasket can be had for a few hundred bucks.
How many miles since last Tranny service? If more than 33kMiles, I'd first try that:
PanDrop & ATFDrain, ValveBody bolt retorq, new Filter, Band adjustment, new PanGasket, fresh MerconV ATF.

 

I don’t know how long it has been but I just bought it and I drained it and torqued all the bolts back because they were all loose then I put new filter on and gasket on pan and filled back up. The transmission was doing it before then as well. It doesn’t do it all the time and when it does I pull over shut it off and start it back and drive. I ordered a scanner for transmission hopefully it will spit a code and I can fix it myself

 

I believe 1998 was well before the BondedGasket was available for the 5r55e ValveBody,
so if Tranny has never been serviced or worked on, it likely still has the un-improved gasket.
The loose VB bolts that you found may have caused or contributed to a blown out gasket.
5r55e Transmissions seem to rarely go beyond 150k~200kMiles if they've never been serviced.
ValveBody could also have a worn out solenoid. Your scanner should give you some specifics.
You may get lucky & only need a Gasket or Solenoid or rebuilt VB,
or it could require a full Tranny rebuild.

 

Ok so I ordered the computer and my truck is throwing codes: p1703 p1780 and p1127 I got the o2 sensor but now I’m trying to figure out what else to do I went to AutoZone and advanced and no one can get a transmission control module. Also my overdrive switch doesn’t work and I can’t seem to find one of those either. I have a 03 ranger I just flipped that was perfect I put 235,000 miles on it and never had a serious issue with it but it’s a manual. I also have a 00 ranger that has 150,000 miles on it. I bought it back in the spring for $500 and it’s a really good truck I drove it home but frame was rusted in half. Will a automatic transmission in my 00 bolt up to my 98 both 4.0?

 

Yes, a 2000 4.0l trans can be used in a 1998 4.0l vehicle, assuming both are 2WD or both 4x4s

 

So the only codes that it is throwing are all codes that I replaced the part for like p1703 brake switch
P1780 transmission control o/d cancel circuit out of self test
p1705 TR sensor out of self test
p1501 vehicle speed sensor
I replaced all of these and it’s still saying it idk?