I have a 2005 F250 6.0l. I have no speedo and the ABS light is on. It was intermittent at first. It would go on and off if I hit a bump or braked quickly, but now for the last month the light has been on constantly.

I have tried the following to no avail:
1. check the harness to the VSS (rear ABS senor on the pumpkin)
2. replaced the VSS on the rear
3. check the lines from the vss for resistance and open short (and short to ground)
4. checked the HS-can network (pins 14 and 6 in the DLC to the respective HS-can + and - on the module) both have less than 5 ohms (about 3 ohms found) and no short.
5. checked the resistance of the network itself across pin 4-16 and found 60 ohms.
6. ran scans with OBD fusion for ABS (no abs found)
7. ran scans with forscan with laptop, does not detect ABS unit neither new or old module. note the TBC and IC both throw codes about not detecting the ABS.
8. check HS-can on the PCM as well as VSS wire from abs to pcm, no shorts or resistance.
9. check the number 11 fuse, (good) checked ALL fuses, only bad fuse found was trailer light number 20 engine bay. issue was a wire at the tailer connector was t-taped and not sealed leading to a short to frame.
10. checked the connector to the ABS module for power on both constant power pins, for open ground on both grounds, and power on run, all with in spec.

I've been diagnosing this for the last week, I am running out of things I can think of to check.

 

Remote possibility, though does not explain speedo:

Might be time to replace the rear brake hoses, all three. So you might as well do the front brake hoses, add SpeedBleeders to the four calipers and flush out the entire brake system with fresh fluid.

 

a good preventative tip. but I think i have a electrical issue since I have u1900 codes and p0500 code which i forgot to mention

 

Edit: bad link

Try this link very similar. Also tells how to read ABS in ForScan.

 

Umm, the link seems incorrect. I got a 20x20 pixel gif file. Confused @.@

 

That changes everything - brake pedal sensor and wire, gray with black tracer. Is probably grounded short.

 

https://www.ford-trucks.com/forums/1...p-working.html

Sorry, try this.

 

from the wire diagrams I have, there is no brake pedal sensor wire connecting to the ABS module. just the following connections

-(3) pair of sensor leads to the abs wheel speed sensors (hall effect)
-2 chassis ground
-2 constant power
-power on run
-VSS signal (grey/black) (the abs creates the VSS signal based on the ABS speed sensors)
-HS-CAN +
-HS-CAN -

the VSS wire I have checked for open fault and power fault (grey/black)

where should I be looking for the brake pedal sensor to connect to? PCM?

 

Yes. I'll find the link. If shorted then cascading impact exactly as you have described and validated.

This might help:

https://www.ford-trucks.com/forums/1...elp-of-ae.html

 

I remember looking at that thread awhile ago. I have 0 mph from IC and PCM but I cannot connect to the ABS module in FORscan. the ABS module does not even show up on the list of modules. I have tried a couple of used ABS modules but still cannot communicate with the ABS

 

87crewdually, wrote that. Maybe he'll see this and point you in the direction on how to read it. I have ForScan on a laptop at the shop if he doesn't come on I'll look tomorrow.

 

Not getting communication at all? It seems that you did your homework and checked some things out. I'd have to double check. It seems that the ABS module may be faulty but you said you tried a couple of others and still no talking to the PCM. So I'm wondering if it's on the PCM side?
​(Thinkin out loud here^​​​​​)

 

It's certainly possible. I don't have another pcm to try unfortunately. The way I understand the trucks computer architecture: there are the two busses (ms-can and HS-can) connect directly to the dlc (obd2) port. And each module connects to those busses in parallel. So if I am reading a abs fault from the tbc module and the IC module as well. then I'm not sure if the pcm would be the problem. I would disconnect the pcm to diagnosis whether it is adding superfluous noise into the bus but it has one of the two terminating 60ohm resistors (the other one being the ic) if I remove the network would become unstable as the messages would propagate endlessly (i believe)

 

Turns out both the grounds were 15k+ resistance when measured from the chassis with the batteries disconnected. Took awhile was a intermittent failure. Just had to run a new ground from the chassis to the abs ground wires.

 

Did you by chance have a screwy fuel gauge?