I was just writing in someone else's thread about hunting down an ABS light problem.

I could use some help figuring out my ABS system.

As far as I can tell and understand things, the first 7.3 SuperDuty F250s, with four-wheel drive, do not have any front wheel ABS.

The ABS instead uses a signal from the VSS on the rear differential. But for that to work the ABS, there has to be something to compare the speed signal to.

And I think that is a sensor on the transmission?

Do I have that correct?

My ABS light suddenly came on one day about 2 months back. A minute or two later, the speedometer quit working and has never come back. The next time I moved the truck forward from a dead stop, the Overdrive light started blinking, and continues to do this right as I pass 1800 rpm for the first time. Then it just blinks till I turn the truck back off. I have yet to have any success trying to pull out a stored code after several attempts on several scanners.

When I turn the key on, the ABS light comes on right away and never goes out.

I already replaced the VSS. So probably the problem is in the wire going back to the front of the truck ... or whatever else the ABS system works off. ?

More electrical gremlins - the speedometer would only work, sometimes, before this happened. The drier the road conditions, the more likely it would work. After this happened, for a while at least, the speedometer would sometimes work - but only when the road was very wet.

And fun with scanners - years ago, the lower 12v power port would throw a spark when I tried to plug something in to it, and I couldn't get any power out of it either. I never sorted that out and just used the upper port with no issues. Trying to use a scanner, someone asked me if the lowr port worked; I said no. I was informed that the scanners won't work if this power port is not working, and it has it's own fuse. I can't find any blown fuses - and this port works perfectly fine now.

 

The First Gen systems are Rear Wheel ABS Only. 4 Wheel ABS was an Option from the Beginning. Each Wheel has a Sensor generating A/C Voltage.

 

So on my 99.5 I could buy the font abs sensors and just hook them into the wiring plug on the frame rails and onto the font hubs, and have 4 wheel abs without changing the PCM or anything?

OP, by scanner are you referring to a wireless ob2 sending unit to a Torque Pro or ForScan app, or the big dated bulky corded LCD screen units?

 

No. While the wiring is there, the Modulator Valve needs changed. If you could even find one for that era. Perhaps, a later model through 04 would work. But, I can't say for sure. An additional Flash to the PCM would also be required. And, I don't know that there is one for your PCM. You may also have to replace with one for that gen and make modifications.

Again, I have never done this. But, anything is doable with the money and resources.

 

I have the same issue...all four wheels have the sensor. I just replaced front hubs and light came on 4 weeks later. My solution? Pull the bulb this week when I replace dash bulbs LOL I a don't even want to mess with it.

 

I want to just figure the system out. My front hubs have no wiring to them at all, so I am pretty sure I have rear wheel ABS only.

But how does the ABS figure out when to engage? Just the speed data from the VSS doesn't seem like it would be enough.

I suspect the PCM uses a signal from the transmission, and this signal is currently corrupted in some way. How does the trans communicate with the PCM?