redid all the grounds and no fix, thanx for trying.

 

well... I spoke with another mechanic and he said it could be the module that is built into the speedo itself. but this will not take care of the ABS light, will it? im sooo confused! He also said that those are obsolete so if thats the problem then its off to the bone yard. anybody concur with the mechanics idea?

 

Have you checked the voltage at the connector with the key on? should be just a hair under 5v on one pin, and you can check of continuity to ground on the other.

 

would that be at the speed sensor in the diff?

 

Yea, pull the plug with the key on and check with a multimeter

 

Great idea on checking the reference voltage.

Tried to rep you but you know how it goes.

 

Thanks anyways man, its all good. Atleast he can tell if its a sensor/tone ring issue, or something else like wiring

 

ok, probed the plug for the rear diff speed sensor, and it has 11.2vdc on both pins. continuity is there too.

 

umm...wow

You had 11.2v on both? On the sensor, the wire that goes to the pin on the drivers side should be a ground. The wire that goes to the pin on the passenger side should read a ref voltage of just a hair under 5v.
If you are getting 11.2v on both sides, you have a short somewhere. Its not a sensor or tone ring problem.

 

I just went and doublechecked it, both pins are hot. i probed engine running 11.2, and engine off but key on 9.5.
Short, where should i look first?

 

Check the wiring on the frame rail again first, follow it all the way up, looking for anything unusual, especially look around the loom where it comes close to any component that gets hot, around bends or where it is vulnerable to something coming up from the road.
Check that first, i'll do some research and get back to you on what next.

 

thanx, now where finally getting somewhere. i really do appreciate it. i will start reinspecting the wiring.

 

well I had same problem changed (vss) It was fine for couple weeks, now the od light flashes speedo bounces around, air bag light is on, radio will not shut off when key is off, sometimes heater won't shut off too with key out.

 

Ok, bear with me this may be long.

The ABS control module- idk if you know where it is or not, but i'm going to write it all out for the interest of others. Directly to the front of the drivers side battery, near the bottom of the battery, there is the ABS hydraulic control unit, it has the black metal lines coming out of the top of it. The ABS control module is mounted on the front side of the control unit at the bottom, you will hardly be able to see it. Take the forwardmost 8mm fender liner bolt out, and you can work the liner out on the end to where you can see the black ABS control module. The wires will come out of the bottom and into a main wire loom.

Now here are some things to do.

-First, get your manual out and check fuses for anything that has to do with abs or brakes, as well as cruise control and instrument cluster.
-Second, where the drivers side hood strut attaches to the fender. just under that lip about 5-6" towards the rear of the vehicle is an 8mm bolt holding a couple of ground wires on. Take the bolt out, take a file/knife or whatever and scratch the paint just around the bolt hole until you see clean bare metal. Reattache grounds and bolt.
Now go see if that fixed it. I'm not sure if it will or not, but it is a ground wire coming out of the same wire loom that the ABS module is tied into, so its worth a shot.

If that doesn't do anything, then atleast you know you have a good ground for something
Anyways, next take that 8mm fender liner bolt out as I mentioned and get to where you can access the ABS control module. There is a sliding lock that holds the connector to it. Push the connector towards the passenger side of the truck and remove the connector. Check all the wires where they make the turn into the connector where they are not wrapped with a wire loom, it looks like a probable place for chaffing or cuts.
Reinsert connector and check to see if that did anything at all.

If not, unplug the connector again that goes to the module. And unplug the rear VSS.
The 2 wires that go straight from the rear VSS to the control module should be a Red w/pink tracer, and a Light green w/ black tracer.

Now-set your multimeter to ohm setting. Go to the plug at the rear VSS. Put one probe on the red wire, and one on that green one. You should not get a resistance reading, if you do, the wires are shorted together somewhere. Next put one lead on one wire, attach the other to a good ground. Next, do the same with the other. The only one that should have a very low resistance reading(if any) will be the Lt grn one. The red one should read as OL on the meter, meaning open circuit.
Record what you got on all these.

Next go to the plug at the ABS control module. Attach one probe to a good ground, set for ohms, and take a reading on each of the pins, and write down which wires give a low resistance reading(if any) and let me know.
Next-one at a time, put one lead on a pin, and touch the other lead to all the other pins one at a time and write down any wires that give you a resistance reading other than OL.

Thats enough for right know lol, we'll see how far we get with this

 

Ziggy,
this morning i printed out your diagnostic list you gave me and headed out to start on it, i first checked the ground as you had said and that did not fix it. I had already went through the fuses so next i removed all the screws and removed the fender skirt.
I looked up at the ABS unit and to my amazement one of the plugs was unplugged!
So i plugged it in and what do you know, everything works! I new deep down it was something stupid like that. I went out and test drove it and its all good now. I still dont have cruise or my horn but that isnt an issue as much as the abs, speedo and trans light.
I want to thank you for helping me out this way. I use this site alot and it is totally kicks ***!

THANK YOU ZIGGY AND ALL THE OTHER FTE GUYS that help me diagnose this. i am a new to the powerstroke and you guys have babtised me!