99 250 6 speed. Speedometer & odometer quit working. Fuses all check out good. Replaced the VSS on the rear diff & still no luck. Any ideas on what to check next?

Thanks

 

look and see if yours has an output speed sensor in the top of the trans tailshaft.

I've seen this on some trucks.

If you know someone with a scanner that'll do the GEM module, have it scanned for fault codes..

 

Thanks,

It does have a transmission sensor. It appears to be a spring mounted ball bearing push to close circuit. We pulled that out and it check good with the ohm meter. I might try changing that sensor tomorrow if it's not too expensive.

I don't have a scanner, but have been thinking about getting one. Luckily it's a standard so right now I have the guy using a masking tape & marker speedometer labeled:
"x" gear @ "x" rmp = "x" MPH

 

I think that spring mounted ball is the backup lite switch.

 

How nasty was the VSS when you pulled it out?, may be time for diff. lube change. Could be enough gunk built up to prevent it from working. Also check wire from the VSS for a break.

 

The old vss did not look bad. Some minor stuff on it, but no more than would be expected. We traced the wires until they went into the wiring harness. Any idea where the wires come out the other end and what color they are? If I knew that I could check for continuity.

 

Did his speedo and odo stop working all at once or did it act up proir to failing?

 

He never noticed it acting up. He just said as he slowed down for a school zone, he looked down and noticed he was going 0 mph. He reset the trip and has logged about 2/10 of a mile in the last 150 - 200 miles.

 

VSS wire goes into the PCM so you probably traced it as far as you can. Make sure you got a good connection at the sensor. I will assume everthing else on the dash is working. I do remember reading where one member found a loose wire on the back of his dash. ??? don't know about that one. I know for sure I have read about the diff. having enough shaving/gunk in it to foul the sensor. Also the ring that the sensor sees may have something wrong with it. Wish I had more for you. The really smart folks will show up later.

 

Your right. I checked that out after you mentioned this and sure enough it's the reverse lights.

Thanks for the replies Barry. We already pulled the instrument panel to check out the wires. All the other guages, etc. seem to be functioning normally.

 

Unless the diff. fluid has been changed lately, I would go there next. Never hurts to change it once in a while. Once you pull the cover, if there is a problem, you should see it. The only other thing would be a bad sensor out of the box.

 

I'll have to look and see when the last time the fluid was changed. I guess we'll swap the VSS to one of the other trucks next week to rule out a bad sensor, then try changing the diff fluid.

 

Be sure and clean/scrape all the residue and build up out. Be sure you put the right stuff back in there. You'll need to know if and how much fricton mod. to add.

 

Thanks for the tip, but I've got 12 of these PSD's plus a few half tons so I've been down this road before. Now I just print out Guzzle's instructions & then check on the guys every so often.

 

12, wow, what do you do with them? I guess you do have a little experence then.