Speedometer and ABS light
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Speedometer and ABS light
I have a 1993 F150 with a 5.0 V8 and an AOD tranny. I bought this truck to save it from the junk yard. I've done a lot of work to it and have only minor problems remaining.
The ABS light is constantly on when the truck is running.
Also, the speedo doesn't work, but it shows the mileage (and it never changes no matter how far you drive).
I've heard and read that the 2 problems could be connected, but don't know if that's true.
Can anyone offer insights? Such as how to test the VSS? How to test ABS?
The ABS light is constantly on when the truck is running.
Also, the speedo doesn't work, but it shows the mileage (and it never changes no matter how far you drive).
I've heard and read that the 2 problems could be connected, but don't know if that's true.
Can anyone offer insights? Such as how to test the VSS? How to test ABS?
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The ABS doesn't seem to work. I haven't had to do an emergency stop, but I have stopped quickly and it seemed to want to lock up, before I released the pedal. It acted as if it would stand on it's grill if I really wanted to try it.
Fleet Owner
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From: Easton,Ks
More than likely wiring or wire plugs.
Try unplugging the RABS module and see if the Speedometer starts working again.
Most say to replace the VSS generator on the rear end but you never hear of that fixing it.
Yes the Speedometer and RABS run off the same rear end generator.
To check the VSS generator you could unplug the RABS module and the PSOM, put the rear end on jack stands, run it up to about 30 MPH and check the AC voltage under the hood at the RABS plug (photo below) to see if you have approximately 3.5 volts AC.
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Try unplugging the RABS module and see if the Speedometer starts working again.
Most say to replace the VSS generator on the rear end but you never hear of that fixing it.
Yes the Speedometer and RABS run off the same rear end generator.
To check the VSS generator you could unplug the RABS module and the PSOM, put the rear end on jack stands, run it up to about 30 MPH and check the AC voltage under the hood at the RABS plug (photo below) to see if you have approximately 3.5 volts AC.
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Hotshot
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I did what Subford suggested. I discovered that the voltage was not the same with both connected as with the RABS disconnected. There is a voltage drop with both connected. I can't remember the numbers. I have them written down somewhere.
I figured out that the speedometer on my truck works find when the RABS module behind the glove box is disconnected. When its hooked up my speedometer needle wavers at 55+ mph.
I still don't know whats wrong with mine, so the RABS is still disconnected. Mine did this with the old and new PSOM, as well as the old and new VSS.
I figured out that the speedometer on my truck works find when the RABS module behind the glove box is disconnected. When its hooked up my speedometer needle wavers at 55+ mph.
I still don't know whats wrong with mine, so the RABS is still disconnected. Mine did this with the old and new PSOM, as well as the old and new VSS.
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Fleet Owner
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From: Easton,Ks
TexasGuy001,
I have not been able to confirm or verify it but it seems like there are more than one Generator (VSS/RABS) for the rear end and auto parts stores do not have a handle on it.
It looks like there may be one that is just for the RABS and another one for the trucks that have both the RABS module and the PSOM feeding off the generated AC. In other words not all of the sensor generators put out the same current level for the amount of the load (for lack of a better way to say it).
I know that Ford has different part numbers for different years and this may be why.
I have not been able to confirm or verify it but it seems like there are more than one Generator (VSS/RABS) for the rear end and auto parts stores do not have a handle on it.
It looks like there may be one that is just for the RABS and another one for the trucks that have both the RABS module and the PSOM feeding off the generated AC. In other words not all of the sensor generators put out the same current level for the amount of the load (for lack of a better way to say it).
I know that Ford has different part numbers for different years and this may be why.
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TexasGuy001,
I have not been able to confirm or verify it but it seems like there are more than one Generator (VSS/RABS) for the rear end and auto parts stores do not have a handle on it.
It looks like there may be one that is just for the RABS and another one for the trucks that have both the RABS module and the PSOM feeding off the generated AC.
I have not been able to confirm or verify it but it seems like there are more than one Generator (VSS/RABS) for the rear end and auto parts stores do not have a handle on it.
It looks like there may be one that is just for the RABS and another one for the trucks that have both the RABS module and the PSOM feeding off the generated AC.
I haven't really looked into it though so I can't tell you whether the current output was different or not.
Hotshot
Joined: Sep 2001
Posts: 11,958
Likes: 228
TexasGuy001,
I have not been able to confirm or verify it but it seems like there are more than one Generator (VSS/RABS) for the rear end and auto parts stores do not have a handle on it.
It looks like there may be one that is just for the RABS and another one for the trucks that have both the RABS module and the PSOM feeding off the generated AC. In other words not all of the sensor generators put out the same current level for the amount of the load (for lack of a better way to say it).
I know that Ford has different part numbers for different years and this may be why.
I have not been able to confirm or verify it but it seems like there are more than one Generator (VSS/RABS) for the rear end and auto parts stores do not have a handle on it.
It looks like there may be one that is just for the RABS and another one for the trucks that have both the RABS module and the PSOM feeding off the generated AC. In other words not all of the sensor generators put out the same current level for the amount of the load (for lack of a better way to say it).
I know that Ford has different part numbers for different years and this may be why.
I did have an A'zone Wells brand one before and it didn't help things either. I wish I would have saved the original one when I tried the A'zone one years ago.
Hotshot
Joined: Sep 2001
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The 93 should have had a PSOM as well. Did it have a digital odometer?
Fleet Owner
Joined: Aug 2005
Posts: 23,666
Likes: 301
From: Easton,Ks
1989-1991 had the ABS sensor on the rear end and it only powered (fed) the RABS module. The computer was fed from the VSS on the transmission. So ABS sensor would not have to be as robust as the later VSS. But if these sensors were used in the 1992-1996+ they may not be able to power both the PSOM and the RABS module.
The ABS sensor for 1989-1991 looks the same as the VSS on the 1992-1996+.
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I unplugged the RABS behind the glove box and the ABS light went out. The speedometer and odometer still do not work. I have no way to test the VSS because I live alone and no way to rev the truck to approx. 30 MPH while checking something else.
If I replace the VSS, would I need to replace the one on the rear axle housing or the tranny or both?
If I replace the VSS, would I need to replace the one on the rear axle housing or the tranny or both?