I noticed a few days ago that occassionally my speedo would jump all the way up to 100 and then return back to normal. Today I was offroad and looked down and the thing was going crazy. It jumps all over the place in no relation to the speed that I am actually going. After driving a few more hours, it now hardly ever moves from 0 and my OD light starts flashing after I drive for a few miles. Does this sound like a bad VSS? Would a bad VSS cause the OD light to flash?

 

1. Very possible.

2. Yes, it would.

Have your codes read to verify what the computer thinks is wrong, then proceed with diagnostics.

Steve

 

why cant they still make speedo cables the way they always have??? remember the days when all u had to do was pull the old one off, buy a new cable grease it up, throw it back in your done. o well sign of the times right.

 

Get the codes scanned and go from there.

 

VSS (Vinovka Snaiperskaja Spetsialnaya = Special Sniper Rifle)


check the codes,becareful driving until you know what it is,,The transmission needs to know the vehicle's over-the-road speed to know when to shift gears properly. dont want to mess anything up

 

You can get the codes read at Advanced Auto, or an Auto Zone for free. You could be getting a P0503: Intermittent Vehicle Speed. It may also cause your truck to shift very hard in 1-2 gears. I changed mine last week, and it cost $18 and took about 5 mins. See my last post. Good Luck!

 

Speedo cables are like carburetors - absolute antiques, and that's where they belong. Too bad Ford went BACK to plastic gears. IDK why they didn't keep using the ABS sensors like '92-96 trucks.

 

Surprisingly, my truck seems to be running exceptionally well with the speedo out of commission. I also noticed that my odometer randomly turns off completely. If I flick the trip button once or twice it will turn back on. This is probably expected, but the odometer doesn't record the mileage when the speedo is not working. Some of you may have read my other threads and if you have, you know that I am having quite a few electrical problems with my tranny. I am blowing my PCM fuse, my transmission fuse, and my OD switch fuse, under heavy acceleration. Now my odometer isn't working properly and my speedo stopped working. I am having a hard time believing that these are not all related, but I have found no evidence that they are. I am not exactly up to the task of going through all the wiring, but I will get the codes read soon and post them up here. Thanks for all the replies.

 

Alright I know you guys said to have the codes read, but I have been very busy starting a new job and such so I haven't had the chance. What I did do, however, is pull what I thought was the VSS from a used 4R70W (same as I have) and put it in my truck. Still no speedo. I have read a lot about the VSS having poorly made plastic gears on the end. What I changed was just a small plastic sensor with a magnet on the end. Next to the tranny that I pulled this sensor from was a tranny from a Thunderbird which looked exactly like the 4R70W, but was not labeled. The Thunderbird transmission had the same sensor that I pulled, along with another one near the very back. I pulled that one out and it was exactly what you guys were talking about: about 5 inches long with a small plastic gear on the end. I checked the 4R70W for that sensor, and there was a spot for it to go in, but there was just a plastic cover over it. So is what I changed the VSS? If not, then where is mine located exactly? And if so, what else could cause the speedo and odometer to go out?

 

That was the OSS (#101 in this diagram).



The VSS is further back on the tailhousing.

.

 

If your transmission is not exhibiting any drivability symptoms, then the PCM is probably getting the correct VSS signal.

Your odometer blackout problem indicates you have a cluster problem, not a VSS problem. This, of course, is based on the additional information you've provided that was not available previously.

Steve

 

If you have a 2002 truck, then you don't have the plastic VSS gear that I think you are referring to... Where you say you have a plastic cover on your trans near the tail shaft is where this actual VSS gear went on the 97-98 models. 99 and after is all electronic and there is no physical gear anymore.

Basically, if you have a digital odo, then you have no VSS gear as such...

I'm not sure what drives the speedo/odo on your truck, but it's electronic and probably inside the trans.

Since you are having all the electrical issues you state with your trans, I'm sure this issue is just another 'victim' of that... You might have a gotten the main wire harness connections wet that go to/from the trans?? That could short out some connections and causing the problems you say you are having...

Good luck!

Mitch

 

Okay I'm much less confused now. I work at an auto salvage yard so I'll just swap my whole instrument cluster with another one and see if that helps anything. Thanks a lot.

 

THAT will open a whole different can of worms if you're PATS equipped.....


Steve

 

Alright well then what's my best course of action here? Wait, let me guess: get the codes read?