Speedo and flashing OD light? Related?

[tdnp]

My 99 f-250 superduty 7.3 OD light is blinking and the Speedometer does not start working until about 20mph? Could these be related?

What should I have scanned the PCM or the GEM?

HELP.

Thanks

[MtPaul401]

Probably rear differential speed sensor, same thing happened to me last summer. Part is around $20 at Napa or Ford.

[tdnp]

Rear diff speed sensor? Where is it at? I just replaced the ABS sensor and I do not remember another on the rear diff? I will look again. Thanks.

[ROLLINCOAL007.3]

It's on top of the rear end... same thing happen to me last week...

[szyd]

Originally Posted by tdnp

Rear diff speed sensor? Where is it at? I just replaced the ABS sensor and I do not remember another on the rear diff? I will look again. Thanks.

That is it. check conection makesure the weather pack is there.