Is it the VSS or PSOM?
 

Howdy folks. Buddy has a 2000 F-350 V10, automatic 4x4. Problem is, his speedo won't work all the time and the OD light will flash, indicating a problem. I know it's VSS or PSOM related, but the thing is, the transmission shifts normal. Any other Ford truck I've seen have this problem, it will shift hard enough to break your neck.

So do you suspect that the PSOM module could be going bad? The Speedometer works most of the time, but sometimes it wont. I'm thinking bad PSOM, what do you think?

Well it would be cheaper to change the VSS sensor first in the rear diff.
Change that first!
any abs lights flickering at all ?

Psom??? you want to clue me in on what it is ?
Do you mean PCM?
Rich

the VSS going out is a very common problem on ford trucks and SUV,s (must of been designed buy the same guy who designed the cam sensor) try that first, odds are thats the problem

Programmable Speedometer and Odometer Module. It is essentially the circuit board mounted on the backside of the speedometer. I know 92-96 F-series had these, not sure about newer ones though.

The new ones don't have them they have a instrument cluster modulethe entire instrument cluster has to be changed.
Thanks for cluing me in on his acronym.
Rich

Could the VSS also cause a random miss? Mine has a miss along with the speedo dropping and ABS light coming on. All COP, plugs, and boots have less than 5000 miles. One boot was changed again less than 500 miles ago. I still have an irritating miss. The local shop has given up on it. Then the VSS symtoms starting happening recently. Could they be related?

Mike,
I don't think they're related. Did you install dual alternators or modify the charging system in anyway? Have you had a diagnostic ran on the engine (you said the shop gave up, but did not say what method they used)?

Usually the ABS coming on is associated with the VSS - the miss, imo, is another thing altogether.

Mike ,we did if I remeber correctly have a guy have some wierd situation cleared up by changing his VSS. And I think it was a misfire code or something.

By all means computers as suseptable to interference. If the vss is causing a malfunction, could it cause something to go haywire maybe.

Change the VSS on your vehicle and see if it goes away.
Rich

Mr big we had someone awhile back with a simalar post about 2 yrs.

You can remember that far back? I can hardly remember what I had for breakfast...

Thanks for the heads up, Rich. I'm gonna follow this one... :-X22

I think its heading downhill....

I just went out & changed the sensor. Still get ABS light flash on occasionally, speedo drop, and the miss. In addition, it felt like the truck wanted to pull to the right on hard braking---sort of like old drum brakes when they get wet. First time thats happend. That HAS to be an ABS problem, right?

Still don't know what to do about that miss.

No mods of any kind. The shop just told me their system did not detect any codes. I have no idea how modern their equipment is, but they were able to pinpoint a miss last year when we did the full tune-up. This time, they pulled and checked each COP, plug & boot. One boot looked "rusty" so they changed it. That seemed to work for a day or so, or at least I did not feel a miss. Then the miss returned along with the symtoms of a failing VSS. The shop kept it for another two days then told me to come get it.

Woulda-shoulda-coulda replaced all the boots, but they didn't. I know it's about to drive you crazy, Mike, but I think it must be something related to the COPS/Boots.

However, like FortyFords said - one person changed the VSS and all was well - you never know.

I think I remember you having a 4x4 ESOF. Is that right? Have you checked the ABS sensors up front? I know it's a long shot and Rich may scold me, but I'm almost out of ideas. Maybe the signals to the PCM from the GEM is causing a problem.

Sorry I couldn't be of help further....

Yea, should have changed them all. But dang, its only been a few months...

Yes, I have the 4x4 ESOF. I'll look at the front sensors next.

My apologies to handyman for inadvertently hijacking your thread.

Well Mr big and Mike,the analogy I have is that I got this reversed in my old mind.
It was a post about bad cops causing misfires causing the pcm to malfunction in someway internally.The guy either changed the cops or swapped pcms and it went away. Sorry about the confusion .As has been talked about the vss is usually the culprit. There can be internal tranny problems that act like a miss(studard or slippage)
and also give the flashing overdrive light.

Now a real good shop should have a computer hook up to determine which cops are bad or misfiring.
Mike when you changed the vss sensor did you reset your pcm by unhooking the battery to alow the pcm to relearn and clear any codes?
was your old sensor covered in grayish particles ?

If you had abs problems there would be a solid abs light on. and there would be codes stored in the pcm (need scan tool to get them)
Here is a test disconnect the wheel sensors and see if you get a solid abs on
You will have to reset (unhook bat) for about 10 mins
after to clear,
Rich

I would say start with the vss.