95 f150 254k (NOW SHOWING 240k!!) 5.8

Ok what just happened. Driving at 35 mph and I can feel the shifting going out like it was trying to downshift from 4th to idle. Speedometer flatlined at zero and the odometer went BLANK. I gave it has and only the RPMs shot up like I was in idle. I pulled over but kept it rolling around 10mph and then the speedometer kicked back in and the odometer was reading again. NO CEL OR VOLTAGE DROP ON DASH.

KOEO: 111 CM: 211 (still chasing)

KOER: 111

Speed sensor maybe? The fact that the odo completely went blank is weird though.

I read online that a guy found it to be a blown 15A fuse, guess I'll check that in the morning. I'm just confused why it all started working again...

All the fuses are fine, truck is running normal for now...

Wiggle test might not be a bad idea. Get a helper to watch the odometer, then crawl underneath. Start at the speed sensor on top of the rear axle. Grab the wiring harness connector and wiggle it. Move along the wiring harness down the frame rail, where the wiring harness goes into the trans on the passenger side, at the mlps where the shifter cable hooks up on the driver side, where the harness transitions from the frame to the body, at the firewall where it connects to the computer.

Corrosion underneath the fuse panel under the hood is common, also. It`s not sealed. Don`t forget the body grounds. Just work your way along moving/wiggling the connectors and wiring harness.

Wiggle your ignition switch had a 97 F250 that the switch contacts went bad in. It would kill the speedometer.

Thanks guys, I'll do some wiggle tests and check grounds.

Thanks!

UPDATE

I haven't found anything with the wiring yet but it happened again today, this time stayed failed for 10 minutes while I limped it home and the o/d light started to blink (yay?) a code! KOEO 452 VSS signal too small. Again it randomly came back right when I pulled into my neighborhood so I'm thinking this has to be an intermittent short because it can't be a fuse or bad sensor at this point?

Could it be a dirty VSS in the pumpkin?

Yes, this is symptomatic to the speed sensor on the rear differential. Sometimes they go out. They can get a little water in them and throw off the voltage.

Try replacing that before you assume there is a short somewhere.

Ryan

The vehicle speed sensor (VSS) in your truck is used in many different Ford trucks/SUV's and the signal produced by it is used by a variety of things (ECM, tranny shifting, speedo/odo, cruise, ABS, etc) in the the vehicle. It is also a very well known fact that sometimes when the VSS fails, some items that use data from it will work fine and others will not. Additionally, sometimes there will be a DTC (as your vehicle has kicked up), but sometimes not. So with this in mind, this is one of those times where the next step is to drop $20 on the part and 10-30min of time to replace it. Don't forget to clear DTC's after performing the repair, which can be done by pulling a battery cable for 5 min (30m is really better).

Dave here, may try and hijack thread. I have a 99 F250 7.3. Same, speed odmeter quit, RPM still works, ABS light on, and over drive light blinks. I did change sensor in the Diff, did nothing and read the the "output speed sensor" , is on rear top of transmission?? Where is the best place to buy one? Read somewhere online but now can't find it. Any ideas appreciates. Thanks Dave

Hi, I had a 02 F250 7.3 that did nearly all the same things, I had an alternator putting out too high of voltage occasionally .. problem confused me for almost a year

98 k2500 6.5TD 4x4 ext cab boss v plow (no muffler or soot filter, pmd relocate I think, k and n air filter) known mods

2000 F350 crew cab dually 7.3 powerstroke

Thanks for the replies. I will try to clean the sensor first and replace if it repeats. Would a sensor go in and out like I'm seeing?

Damien, good call on the alternator. I've been keeping a good eye on it as it is the original and I do see weird voltage readings on my dash almost daily, but of course passes everytime I test it. Something worth thinking about.

fordgirl said:

Thanks for the replies. I will try to clean the sensor first and replace if it repeats. Would a sensor go in and out like I'm seeing?

Damien, good call on the alternator. I've been keeping a good eye on it as it is the original and I do see weird voltage readings on my dash almost daily, but of course passes everytime I test it. Something worth thinking about.

Click to expand...

If I recall correctly, the sensor has one very small bolt holding it in. At that point is slides out. It may not easily "slide" if there is a lot of gunk and it's been there for 20+ years, but you know what I mean by "slide." There's nothing else holding it in.

Ryan

Dave Tyler said:

Dave here, may try and hijack thread. I have a 99 F250 7.3. Same, speed odmeter quit, RPM still works, ABS light on, and over drive light blinks. I did change sensor in the Diff, did nothing and read the the "output speed sensor" , is on rear top of transmission?? Where is the best place to buy one? Read somewhere online but now can't find it. Any ideas appreciates. Thanks Dave

Click to expand...

I'm not sure which transmission you have, and how the diesel may have a different set up than the F-150's, but some of the earlier models had speed sensors on the transmissions in F150's. It's entirely possible.

2 locations on speed sensors, on the rear differential right above where the driveshaft connects, and on some models, on the transmission.

Ryan

fordgirl said:

Thanks for the replies. I will try to clean the sensor first and replace if it repeats. Would a sensor go in and out like I'm seeing?

Damien, good call on the alternator. I've been keeping a good eye on it as it is the original and I do see weird voltage readings on my dash almost daily, but of course passes everytime I test it. Something worth thinking about.

Click to expand...

Mine never showed any signs until I took it off, took it to store and tested it there, bought a new one and no longer has issues

98 k2500 6.5TD 4x4 ext cab boss v plow (no muffler or soot filter, pmd relocate I think, k and n air filter) known mods

2000 F350 crew cab dually 7.3 powerstroke

I did a wiggle check with no faults so I took the sensor off and cleaned it, day 1 is good so far!

So that lasted weeks but then it hard failed with the same code for VSS. So I replaced the sensor and it still isn't working! Took it for a drive and sure enough, same VSS code.

Can I have damaged teeth/gear that is causing the sensor to not get a good read? Or how about really dirty diff fluid that has too many shards of metal?? I'm trying to figure out where to start next and I'm thinking to drain the diff and look for damage.

Gears look good, no metal pieces found. I guess I'll be looking into wiring and PSOM...