Whats going on with my Truck. Coming back from Vac. the Odometer started to drop off and on from around 70mph to 40mph. It would not start to read until I got up to about 35mph.
Also the Overdrive light on the shifter would blink from a dead stop until it went through the gears. To start off these misterious things the ABS light came on. Can anyone help?

 

Possibly the speed sensor on top of the rear differential is going out or there is a loose connection.

 

I had a similar problem on my '99 F350.

There is a 3 wire twisted harness that routes through the shifter tube to the OD on/off switch. The wires were routed such that they rubbed on the shifter boot bracket. 3 screws hold the steering column cover on. Remove this, and the wiring is easily visible. I had to unplug the wiring, remove the shift lever, and repair them. It took about 20 minutes, and all was well again.

 

I had same problem on my '99 F-250. It would be your speed sensor located on top of rear diff. I asked same ? about a month ago and got a quick and accurate response. The part cost $15-18 and takes about 15 min to install. Just don't get any dirt in the rearend (not good). best of luck and enjoy working on your truck!

 

Have similar problem. Just installed the Tymar Air Intake System this past weekend. Shortly thereafter I started having the follwing problems:
1) ABS Light stays on.
2) Service Eng Soon Light stays on
3) Next day, the Overdrive Off Light flickers on & off constantly.
4) Odometer needle flutters ,,, and drops to zero when i let off the gas (even if costing 20+ mph.
Could I have bumped something at install time?
Could the on board computer be going crazy since I disconnected the drivers side battery only ........ should i diconnect both batteries and see if the computer resets?
Any help is appreciated.

 

I dont think disconnecting one battery versus both will make any difference, as that they are in parallel. What year is it?

 

Early 99' F350 7.3 Crew Cab 4x4.

 

Speedometers are over rated anyway...

 

Hello Guys,
Thanks alot for Info. It was the speed sesnor located on top of the rear end.
Thanks.

 

Apparently this speed sensor causes havoc to the computer. See my problem logged under " Warning Lights Going Crazy After Tymar Install"!
My problem had nothing to do with the Tymar Air Intake install ... just a coincidence that the speed sensor went out at the same time.
Had ABS, Service Engine Soon, and Overdirive lights on which left me chasing several ghosts all caused by this one sensor.

BEWARE to all!