Looks like I may have to replace the PSOM on my 1994 Bronco. Speedometer has a tach. My question: Will the speedometer cluster from a 1995 Ford 150 without a tach work if I just replace the microprocessor that sits behind the speedometer? Does the microprocessor also run the tach?

 

Yes the PSOM from the 95 will work. The tach is independent of the PSOM. Remember too that if you need to reprogram the PSOM for mileage or changes in gear ratios/tire sizes, you only get six tries. After that the microprocessor won't accept any further changes.

 

Put the PSOM in and so far the truck shifts fine. Thanks for the heads up on the '95 unit working in this truck. Didn't realize so much dirt and grime got behind the dash and am curious if this was part of the problem. Will know more in coming days because the problem is heat related and it's suppose to be hot tomorrow. Any idea on how I program this unit since the miles currently exceed the original one I took out of the truck.

 

Do a search of the tech articles here. there is an article specifically detailing the procedure for reprogramming the PSOM

 

How was the trans acting before? How did you know that the PSOM was the problem? Any other symptoms?
My E4OD is shifting hard, i've replaced the VSS and MLPS and it is still doing it. I have no trans codes just code 452 VSS/PSOM. I can't figure it out.

Thanks,
-Greg

 

I had a 452 code too. Tranny shifted hard sometimes, sometimes it didn't. Seemed to be heat related. I simply took the cluster out of the dash, then took apart the cluster to get at the speedometer component. The local junk yard had the speedo for $25. I believe speedos from 1992 - 1996 will work from F150s and Broncos. I had no idea the speedo could make the tranny do this, but I do now.

 

Thanks kpoly2,

I found a topic showing how to check the PSOM electrically by locating a spade connector under the dash. I checked it and i got a constant 5 volts, which means that the PSOM is good and the VSS is bad (if the PSOM is bad there should be no voltage). I unplugged the VSS and immediately got the ABS light on my dash, plugged it back in and it went away. So i think that tells me that the VSS is good(I just replaced it last week). I disconnected the battery for 20 minutes and i tried to readjust the MLPS on the trans.
I connected the battery and the truck drove great. I thought i had finally fixed it. But no, after about 10 miles it began shifting hard again. I don't know if i reset the computer and it had to find the error again, or maybe the truck just got warm and the problem came back, or maybe the MLPS is still the problem(it's new, but i couldn't pull the wires out for the new connector, it was updated by previous owner, its just dirty).
It still sounds similar to your problem, so i may just change the PSOM anyway.
-Greg

 

I went ahead and replaced my PSOM and the problem is gone. Truck shifts great now!

-Greg

 

Great! Hope this fixes your problem because it did mine and my truck is shifting fine.

 

I have a 1994 f150 with E4OD. shifts hard. has new vss / pcm. still having same problem. speedometer works fine but scan code will occasionaly give a vss code. Can you tll me if the PSOM is part of the speedometer instument cluster or is it a seperate part. thanks

 

PSOM is an acronym for Programmable Speedometer/Odometer Module.

 

Yes, the PSOM is part of the instrument cluster. It is a circuit board inside of the cluster. It can be seperated from the cluster by taking it apart.

-Greg

 

Found the test spade for the PSOM had 4.75 volts at idle and while driving. The truck did not shift hard while checking voltage. I had the battery disconnected just before i checked for voltage. I am going to check it agian tomorrow while driving.

 

I checked the voltage at that spade connector too. Even when it was acting up, it still read a constant ~4.5 volts. I heard that this meant the PSOM was good, but i replaced it anyway and it took care of the problem.

-Greg

 

Thanks for the info. I think the PSOM is the next step