92 F150 :Lost speedometer and odometer display
 

I was on my way to the emissions center to get my emissions test and when waiting in line----I noticed that the electric odometer display was blank-no characters at all. I also noticed that the speedometer pointer doesn't move. :-hair

I was able to pass the emissions test without the speedometer/odometer. I checked for DTC-there isn't any.

I checked in the Shop Manual and it states to depress the RESET button at the same time as turning on the ignition switch. And then release the RESET button. After doing this-still no odometer display. And the speedometer pointer should sweep when depressing the RESET button and turning the ignition switch on-the pointer doesn't move at all.

The Shop Manual says to replace the instrument cluster!! How can this failure occur ?

I also disconnected the negative terminal of the battery-just to see if the PSOM would reset---the speedo and odometer is still non operative.

The Shop Manual suggest that the speed sensor in the rear axle wouldnt be the problem because there isnt a digital display on the odometer and because the speedometer pointer doesn't sweep on the "RESET button depressed/ignition switch on" test .

What else can I check?

Please-someone tell me that there is another way to correct this issue without replacing the Instrument cluster!

Check the fuse for the PSOM, then check the wiring feeding it, you obviously have no energy going to it for one cause or another. Since the odometer isn't turning on you can rule the VSS or its wiring as the causes.

Check fuses 8 and 18. Does the dome light work? If not Fuse 8 is probably out (it also supplies power to the PSOM).

Otherwise you probably have Fuse 18 open or an open circuit.

The dome light does work. I see that fuse 18 also serves the speed control. I will check fuse 18 when I have access to the truck again. I have access to the Shop Manual but not the truck at this time. And I didn't have access to the owners manual when I originally posted.The Shop manual says to check for battery on the PSOM pin 1-but doesn't state what fuse is involved in the circuit and I don't have a circuit diagram.

If the fuse blows after it is replaced-I would suspect that the clock spring for the speed control or the speed control circuit may be the source of the trouble.

Would you all agree-- that because I am not getting any digital characters at all on the odometer display-that the trouble can't be in the speed sensor on the rear axle?

There is no clock spring for the PSOM.

I am aware of that. But the cruise control is protected by the same fuse and if the new fuse blows- the CC may be the source of the problem.

Correct, speed sensor ain't the problem.

Agreed.

You can usually tell why a fuse failed... if you look in the side of it and see black deposits (like an arc flash would leave) then it blew due to the large fault current caused by a short.

If the wire inside is broken/melted, but not vaporized, then it blew due to a moderate overload over time.

This method ain't 100% accurate but it should give you an idea. :-X22

Amazing info dixie :).

My dead PSOM wasn't caused by open fuses 8 nor 18. Have to get into the instrument panel and check for battery on pin 1 -I guess.

It couldn't be an easily fixed problem.

The Ford dealer parts guy laughed when I asked if it is possible to get a replacement from them---or if there is a contractor that will fix them.

Is the total odometer mileage in the speedo/PSOM head itself--or in the main computer of the truck? I just hate not having the actual mileage displayed on the odometer.

The mileage is stored in the PSOM.... You can change speedometers and keep the original mileage by using your old PSOM..

So--the PSOM and the speedometer head are separate ?

Do you have the part numbers for the PSOM and speedometer head? I would like to search nationally dealer stock and see if these would be available New-Old-Stock.

Appreciate you help and advice!

I think these have been out of stock for quite a while now, but you can try looking for one, just don't get your hopes too high. NumberDummy is the go-to guy if you want the part number for you PSOM, seek him out and try a PM.

Yes, they're separate deals, but on the same power circuit from the fuse panel at your left knee.

Only place you will find a PSOM is a Pick a Part(junkyard). If the both fuses are good, then most likely the PSOM failed. Mileage and pinion factor are stored on the PSOM's circuit board EEPROM. I am successful in swapping EEPROMs from the Pcboards to keep my mileage and pinion factors but you must know how to unsolder a dual layer PCB without heat killing the EEPROM!

If you don't have a tach cluster, nows the chance to get one. Its plug and play with 92 to 93 trucks(gas only). If not then you will have to take the cluster apart to get the PSOM(speedo) out.

Also the cruse control will not function without the PSOM sending it speed info. You may have driveablity issues too as the ECU is not getting speed info expecily if you have the E4OD automatic. With a 5sp manual, you'll get some wierd idling down issues while coasting.

Help me understand---is the PSOM actually part of the speedometer head? If not-where is it located?What does it look like? Is it located within the instrument panel assembly? The PSOM is the actual solid state part of the speedometer assembly? I am having a hard time visualizing what the PSOM looks like and where it is located.

So the actual total mileage info is located within the PSOM memory? And it cant be changed to reflect the actual mileage of the new truck that it is placed in after removal from the donor truck?