Transmission issue
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Mountain Pass
Joined: Jan 2005
Posts: 112
Likes: 1
From: East Tennessee
Transmission issue
I have a 1995 F150 XLT 4x4 5.0 Auto. The trans was rebuilt in 2010. On the way to work this morning the OD OFF light on the gear shifter was flashing. The truck felt like it was not going into overdrive. The speedometer and digital odometer had both stopped working too. I pulled over and put the truck in park and then back in gear. It seemed to start going into overdrive as it should, but the light kept flashing and still no speedometer or odometer. Anybody got any ideas? Any help would be greatly appreciated.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Check Fuse 18 in the fuse box inside the cab. It supplies voltage to the PSOM and other functions with the key in the Run position. Fuse 8 supplies power to the same PSOM at all times. Check both.
Postmaster
Joined: Nov 2011
Posts: 3,533
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From: SW Florida
To explain rla's answer better, them fuses power the PSOM (Programmable Speedometer/Odometer Module) which is what takes the speed data from the VSS (vehicle speed sensor) and conditions/calibrates it before sending it to the EEC (Electronic Engine Controller) which is the computer that runs the engine and transmission.
When the PSOM goes dead (you can tell when this happens because the speedometer quits as well), the EEC stops receiving speed data and won't know exactly when to shift the transmission based on ground speed, so it uses a predefined set of parameters instead. It also sets a fault code in memory indicating the APPARENT problem (not necessarily the actual cause of the problem) and for faults that affect transmission operation, it will also flash the OD OFF light to indicate this.
Check your fuses and get back to us.
When the PSOM goes dead (you can tell when this happens because the speedometer quits as well), the EEC stops receiving speed data and won't know exactly when to shift the transmission based on ground speed, so it uses a predefined set of parameters instead. It also sets a fault code in memory indicating the APPARENT problem (not necessarily the actual cause of the problem) and for faults that affect transmission operation, it will also flash the OD OFF light to indicate this.
Check your fuses and get back to us.
Thread Starter
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Mountain Pass
Joined: Jan 2005
Posts: 112
Likes: 1
From: East Tennessee
#8 fuse was blown. I replaced it and the OD OFF light is no longer flashing and the digital odometer is working again. I'm still at work so I haven't driven it yet to check the speedometer and see if it shifts properly. Thank you for the information rla2005. If that's all the problem is, I'll be thrilled. This is why I LOVE this forum and recommend it to every Ford owner I know.
Thanks again
blueoval65
Thanks again
blueoval65
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Mountain Pass
Joined: Jan 2005
Posts: 112
Likes: 1
From: East Tennessee
Thanks to dixie460 too. I didn't see your reply before my last post. So if I understand correctly, since the blown fuse would kill the PSOM, that would also explain the trans not going int OD because there is no data going to trans computer to tell it what the ground speed is. I hope I'm gettin that right. (I didn't know what a PSOM was before today) Thanks again for all the information. May God Bless All Y'all!!!
blueoval65
blueoval65
Fleet Owner
Joined: Oct 2005
Posts: 20,789
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From: Kentucky
Great explanation Dixie!
Yes, if the PSOM is dead the computer (PCM) will go into limp mode whcih causes hard and typically late shifts.
What's a PSOM and how do I "P" it?? courtesy of Steve83
Yes, if the PSOM is dead the computer (PCM) will go into limp mode whcih causes hard and typically late shifts.
What's a PSOM and how do I "P" it?? courtesy of Steve83
New User
Joined: May 2020
Posts: 1
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97 F250 speedometer n mileage counter off I checked both 8&18 fuse both ok. Still no fixing
OTE=dixie460;14636852]To explain rla's answer better, them fuses power the PSOM (Programmable Speedometer/Odometer Module) which is what takes the speed data from the VSS (vehicle speed sensor) and conditions/calibrates it before sending it to the EEC (Electronic Engine Controller) which is the computer that runs the engine and transmission.
When the PSOM goes dead (you can tell when this happens because the speedometer quits as well), the EEC stops receiving speed data and won't know exactly when to shift the transmission based on ground speed, so it uses a predefined set of parameters instead. It also sets a fault code in memory indicating the APPARENT problem (not necessarily the actual cause of the problem) and for faults that affect transmission operation, it will also flash the OD OFF light to indicate this.
Check your fuses and get back to us.[/QUOTE]
When the PSOM goes dead (you can tell when this happens because the speedometer quits as well), the EEC stops receiving speed data and won't know exactly when to shift the transmission based on ground speed, so it uses a predefined set of parameters instead. It also sets a fault code in memory indicating the APPARENT problem (not necessarily the actual cause of the problem) and for faults that affect transmission operation, it will also flash the OD OFF light to indicate this.
Check your fuses and get back to us.[/QUOTE]
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