Which speed sensor
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Tuned
Joined: Feb 2022
Posts: 301
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From: Perth Ontario
Which speed sensor
I have a 1996 f150xl 4.9 reg cab 4 wheel drive. My speedo is jumping and hard shift into drive if I put the pedal to it. I was looking at speed sensor on rock auto but there is different one's showing for my truck. Does anyone know which one I'm supposed to get? Thx for the help.
Fleet Owner
Joined: Oct 2005
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From: Kentucky
Before spending money on a new VSS, located on top of the rear axle, inspect the one you have. Carefully unplug it then with even more caution pop it out of the axle assembly. Look for signs of excessive debris and/or signs of gouging/scratches.
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Tuned
Joined: Feb 2022
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From: Perth Ontario
I unplugged the rabs sensor behind the glove box and now it seems to be working fine. I just took it out on the hwy and put it right to boards and no hard shift and needle isn't jumping all over anymore.
Fleet Owner
Joined: Oct 2005
Posts: 20,783
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From: Kentucky
That is the RABS controller and it can cause issues with the VSS signal. A weak VSS signal can also be the cause as well. By unplugging the RABS controller the signal amplitude may return to normal range. So it's your choice to leave the RABS controller unplugged or dive deeper into the true root cause. Many folks do not like the RABS operation on these trucks so you would not be the first to disable it's operation.
Hotshot
Joined: Jun 2015
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Thinking about 1996 technology in vehicles, how would it detect speed from behind the dashboard when it looks nothing like the sensors you were looking at online?
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Tuned
Joined: Feb 2022
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From: Perth Ontario
Sorry I guess it's rabs controller that I unplugged. I guess I said rabs sensor. I didn't do anything with the speed sensor because it fixed the problem. Sorry I got the name mixed up about the thing behind the glove box.
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Tuned
Joined: Feb 2022
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From: Perth Ontario
I don't know how it detects the speed. I just read on this site to try unplugging it and it worked. I'm not a mechanic by any means at all.
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Fleet Owner
Joined: Oct 2005
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From: Kentucky
No worries...plenty of folks have disconnected that RABS controller to fix their bouncing speedometer.
The question becomes is that controller bad or is the VSS signal weak.
The question becomes is that controller bad or is the VSS signal weak.
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Tuned
Joined: Feb 2022
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From: Perth Ontario
There's only po401 and I'm pretty sure it's for the sensor that comes off egr tube with the 2 rubber hoses. Just haven't changed it yet.
does the rabs controller have anything to do with the vss? Maybe whatever that rabs is ,is the problem. ??
does the rabs controller have anything to do with the vss? Maybe whatever that rabs is ,is the problem. ??
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Tuned
Joined: Feb 2022
Posts: 301
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From: Perth Ontario
I was just assuming it was the vss because of the jumping speedo and the hard shift into drive if I was into the pedal. But everything is fine for now anyway after I unplugged the rabs controller.
Fleet Owner
Joined: Oct 2005
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From: Kentucky
Check the silicone hoses that go between the DPFE sensor and the sample tubes on the EGR tube before replacing the DPFE sensor.
Yes the RABS controller uses the same VSS signal from the sensor on the rear axle. As I stated before the RABS controller can be bad with the failure mode it drags down the signal amplitude. Or the other scenario is the VSS signal output is weak. Removing one of the devices in the path restores the signal.
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Tuned
Joined: Feb 2022
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From: Perth Ontario
I have new hoses for it to but the other ones look ok. I no this is getting off topic but if I do have to change the rubber hoses how do you get them on that tube it looks really tight in there?
