speedo problems
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Elder User
Joined: Jul 2007
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From: Lawrenceburg, TN
speedo problems
ok my speedometer hasnt worked right since i bought the truck about 4 weeks ago. it will freeze at a speed ,it will drop to zero ,it will peg all the way over to 90, sometimes the odo goes out sometimes it dont. i thought it was the wheel speed sensor in the rear diff. i pulled it out and inspected it about two weeks ago.it had some metal frags on it and the fluid was nasty. so today i changed the diff fluid and cleaned all the metal out and the speedo still dont work right. so at this point im thinking its the speedo itself or in the wiring somewhere. i still havent totaly ruled out the speed sensor but im thinking they are either a work or not work type thing. i thought it may have been some of the metal frags interfering with it at first but they are all gone now. any ideas on where to go from now. loose ground somwhere?
1997 F250 HD 4x4
1997 F250 HD 4x4
Last edited by 97 HD; Jul 28, 2007 at 10:23 PM.
Post Fiend
Joined: Oct 2003
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From: MICHIGAN
You said you had metal frags on the wheel speed sensor (RABS module or VSS), did you check the tone wheel on the ring gear for bent or missing teeth? IF you can't see it good enough through the RABS module opening you'll need to remove the differential cover again to get a good look at it.
The speedo is a bit more complicated than a signal sent from the RABS to the gage. There is a PSOM (Programable Speedometer/Odometer Module) in there too.
Fuses 8 and 18 protect the PSOM.
There is a ground located Behind the bottom of RH kick panel. The wire is Black with a white tracer.
It splices into the ground for the Speed control servo amplifier assembly (cruise control) and the wire turns into Pink with an Orange tracer. The PCM ground is there too and is routed to the PSOM.
The speedo is a bit more complicated than a signal sent from the RABS to the gage. There is a PSOM (Programable Speedometer/Odometer Module) in there too.
Fuses 8 and 18 protect the PSOM.
There is a ground located Behind the bottom of RH kick panel. The wire is Black with a white tracer.
It splices into the ground for the Speed control servo amplifier assembly (cruise control) and the wire turns into Pink with an Orange tracer. The PCM ground is there too and is routed to the PSOM.
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Elder User
Joined: Jul 2007
Posts: 893
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From: Lawrenceburg, TN
i will probably just replace the sensor and see what happens. i checked all the grounds (thanks cuda) they seem ok. it does seem to be a little better after i changed the fluid and cleaned the sensor.
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Cross-Country
Joined: Feb 2004
Posts: 70
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From: Pennsylvania
Jim, you seem to know alot. My problem is similiar (95 E350 powerstroke). In February cruise kicked off and OD light blinked (and some hard shifting). Independent garage read code and replaced VSS in March. Now speedo needle bounces around a bit (not alot) up around 65 or so (not much at 40). And last weekend the cruise quit and OD light light blinked about 1 hour into trip. Kept towing and 1/2 hour later light went out and towed another 11 hours (5 more out, 6 back) with no light or problems. Took it back to garage and code read VSS again. This time I'm going to learn more about it myself, been reading the threads on here. I'm going to pull VSS and look at condition of rear fluid (154,000 miles, I've owned for last 20,000). But I just went to the dealer to discuss the PSOM replacement and they said there's 2 VSS, one on rear and 1 on trans? What do you know about that? Thanks.
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Post Fiend
Joined: Oct 2003
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From: MICHIGAN
Have you had it scanned? WHat were th codes?
There is only 1 VSS that I know of....in the rear diff. The vans seen to be a different animal though. I will look it up and get back to you.
Check the sensor on the end of the master cylinder (BPA) Brake pedal applied sensor. It's the subject of a recall and will cause the symptoms you described. It causes fires in gassers but NOT in diesels, so don't panic. They still go bad though. Look in the sensor to see if brake fluid has seeped into it.
There is only 1 VSS that I know of....in the rear diff. The vans seen to be a different animal though. I will look it up and get back to you.
Check the sensor on the end of the master cylinder (BPA) Brake pedal applied sensor. It's the subject of a recall and will cause the symptoms you described. It causes fires in gassers but NOT in diesels, so don't panic. They still go bad though. Look in the sensor to see if brake fluid has seeped into it.
Post Fiend
Joined: Oct 2003
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From: MICHIGAN
I just realized that you have a 95. My repair manuals only go back to 96. Do you have a data port connector under th dash, or did they use the data port under the hood. Some 95's have both. If they used the one under the hood, which I firmly believe they did, they the 500 code "Vehicle Speed Sensor" is right but generic. If they used the data port under the dahs, assuming you have one, they will get another code, possibly more codes. Model years 94-96 can be tough to diagnose just because of this. It is when the auto makers switched from OBD1 to OBD2 (On Board Diagnostics). I would go to someone thar specializes in diesels to get the right path to follow. Having said that, I would replace the VSS in the rear diff and the BPA on the master cylinder before having the PSOM serviced.
There is a ground wire for that circuit located behind the dash panel down low. It's on the right side of the steering column. between the column and the engine cover.
There is a ground wire for that circuit located behind the dash panel down low. It's on the right side of the steering column. between the column and the engine cover.
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From: Cincinnati OH
Originally Posted by Cuda_jim
You said you had metal frags on the wheel speed sensor (RABS module or VSS), did you check the tone wheel on the ring gear for bent or missing teeth? IF you can't see it good enough through the RABS module opening you'll need to remove the differential cover again to get a good look at it.
