Bad PSOM Confirmation

[hadley000]

Here's what's up with the old girl now. I drive for 5-6 miles and the odometer goes out, the O/D light flashes and the speedometer is either 0 or pegged. I can feel it starting to act up from the feel of the transmission, it feels like it's dropping in and out of O/D but not getting a light. If I keep driving the odometer and speedo eventually come back and work normally. The tach works fine. I changed out the VSS a while back for another reason, so that's new. I have another Motorcraft one coming just to be sure it's not a junk VSS. I've also checked the wiring from the sensor and everything looks good. It's been parked since this happened more than once to save any trans troubles.

Oh, and the ABS light doesn't come on.

Edit: I pulled the codes, 29 came up, which is "insufficient input from VSS". Could the VSS make the odometer go out, not throw an ABS light, and make the speedo peg in both directions?

Thoughts?

 

[Thewespaul]

Psom will not affect the trans, to me it sounds like you have a wiring issue of a faulty vss. Here is the schematic for the vss circuit so you can check all connections.

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[hadley000]

Thanks for the diagram it helped a lot. I did some more digging and from what I've found it's most likely the VSS. If it were the PSOM I'd have the ABS light on too, which I do not. The needle sweep and odometer display are fine. No corroded connections that I can see, and the wiring is still in good shape. The new sensor will be here tomorrow so I'll see if that works.

 

[riphip]

Thank you for your Service!!!

 

[ifrythings]

If you loose the psom you loose the speed signal to the pcm(or TECA, the trans computer) and cruise control, the abs reads right off of the vss sensor, your vss is fine, leave it alone your chasing the wrong rabbit. The abs and psom are completely separate except they share the vss, one dieing does not effect the other.

Being you loose the odometer I would be looking for either power or ground issues to the psom but the fact you say the speedo pegs out tells me something is not right with the psom board. Does rapping on the dash change anything when it goes dead?

 

[hadley000]

the fact you say the speedo pegs out tells me something is not right with the psom board

It either pegs out or reads 0, but both times the odometer went away. Seems I always have to chase down bad grounds, they are my nemesis. I'll give it another look to see if I can find something.

 

[hadley000]

I found the problem. I forgot to tighten a ground when I put new floorboards and rockers in the truck. It was under the kick panel on the passenger side. It was attached but not tightened down causing an intermittent ground problem. I disconnected it and the odometer went blank. I tightened it back down and it came back, so that was the problem. I feel kind of dumb, lol.

 

[icanfixall]

Glad you found and fixed the issue. Feels great to find and make an easy fix. No reason to feel dumb. Things happen..

 

[YJMike92]

Sounds like something I would do.