OD Light/ Trans Issues
2nd Gear
Joined: Jun 2025
Posts: 2
Likes: 0
Thanks for this info as this may put an end to my issue. New user on FTE! '95 F250 7.3 PSD E4OD with what started as TC unlock/lock issues that would spike 200ish RPM randomly then come back to normal anywhere between 40-60mph has slowly got worse. Last night I experienced erratic shifting and the blinking O/D light w/ a P0500. I've spent hours trying to figure this out just reading the forums & have replaced numerous parts over the years. This issue started 3 weeks ago.
- VSS is New, Pigtail Serviceable. - PSOM Reads speed correctly w/ no bounce & PCM is receiving this data I would assume as I monitor the VSS on OBD and it is always there & accurate. I would then assume PSOM is operating normally.
- ALL NEW ---TPS, MLPS, Baro Sensor, MultiFunction Switch, Incandescent Brake Bulbs, Shifter Bushings, Fresh Mercon & Filter (nothing in filter or pan), PCM Overhauled 1yr Ago, New Valve Body & Solenoid Pack & Harness 1yr Ago.
Mountain Pass
Joined: Dec 2019
Posts: 220
Likes: 13
From: VA
Thanks for this info as this may put an end to my issue. New user on FTE! '95 F250 7.3 PSD E4OD with what started as TC unlock/lock issues that would spike 200ish RPM randomly then come back to normal anywhere between 40-60mph has slowly got worse. Last night I experienced erratic shifting and the blinking O/D light w/ a P0500. I've spent hours trying to figure this out just reading the forums & have replaced numerous parts over the years. This issue started 3 weeks ago.
- VSS is New, Pigtail Serviceable. - PSOM Reads speed correctly w/ no bounce & PCM is receiving this data I would assume as I monitor the VSS on OBD and it is always there & accurate. I would then assume PSOM is operating normally.
- ALL NEW ---TPS, MLPS, Baro Sensor, MultiFunction Switch, Incandescent Brake Bulbs, Shifter Bushings, Fresh Mercon & Filter (nothing in filter or pan), PCM Overhauled 1yr Ago, New Valve Body & Solenoid Pack & Harness 1yr Ago.
I was having the same issue with the P0500 code and assumed my PSOM was working normally. Took the entire dash apart, traced every wire looking for shorts, bad grounds, replaced the VSS, etc. Ended up being a bad PSOM even though everything was seemingly working.
This may not be the case for you, but don’t rule it out. Good luck!
2nd Gear
Joined: Jun 2025
Posts: 2
Likes: 0
I hope you get this figured out!
I was having the same issue with the P0500 code and assumed my PSOM was working normally. Took the entire dash apart, traced every wire looking for shorts, bad grounds, replaced the VSS, etc. Ended up being a bad PSOM even though everything was seemingly working.
This may not be the case for you, but don’t rule it out. Good luck!
I was having the same issue with the P0500 code and assumed my PSOM was working normally. Took the entire dash apart, traced every wire looking for shorts, bad grounds, replaced the VSS, etc. Ended up being a bad PSOM even though everything was seemingly working.
This may not be the case for you, but don’t rule it out. Good luck!
When the truck drives normally I get the VSS through OBD (Direct connection to the PCM). When the transmission acts up, VSS through OBD is lost (0.0MPH) but Speedometer Needle is valid w/ no bouncing. So yup...likely the PSOM not getting that data or intermittently getting the data to the PCM. When VSS OBD is restored, the truck will slam back into gear!
Ultimately, wiring from VSS Sensor to Speedo Needle is good (since needle is always alive & accurate). It's the wiring & or data transfer from PSOM to PCM.
Any good recommendations on PSOM Repair Facilities?
Mountain Pass
Joined: Dec 2019
Posts: 220
Likes: 13
From: VA
Well here's the update for ya! Tested for the AC Ripple from the alternator using a meter as suggested by Mark Kovalsky earlier in this thread. Zeros across the board on both batteries whether hot, cold, idle, 2000RPM. Had O'Reilly Bench it - all normal. They had no issues giving me a new one just to try to see (buddies with them after all...I own a Ford (: ) I was driving it hard to try to get it to act up. Finally, after about an hour of driving, I got it to act up. I pulled over & Plugged in the OBD & pulled up FORScan.
When the truck drives normally I get the VSS through OBD (Direct connection to the PCM). When the transmission acts up, VSS through OBD is lost (0.0MPH) but Speedometer Needle is valid w/ no bouncing. So yup...likely the PSOM not getting that data or intermittently getting the data to the PCM. When VSS OBD is restored, the truck will slam back into gear!
Ultimately, wiring from VSS Sensor to Speedo Needle is good (since needle is always alive & accurate). It's the wiring & or data transfer from PSOM to PCM.
Any good recommendations on PSOM Repair Facilities?
When the truck drives normally I get the VSS through OBD (Direct connection to the PCM). When the transmission acts up, VSS through OBD is lost (0.0MPH) but Speedometer Needle is valid w/ no bouncing. So yup...likely the PSOM not getting that data or intermittently getting the data to the PCM. When VSS OBD is restored, the truck will slam back into gear!
Ultimately, wiring from VSS Sensor to Speedo Needle is good (since needle is always alive & accurate). It's the wiring & or data transfer from PSOM to PCM.
Any good recommendations on PSOM Repair Facilities?
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