I have an intermitent problem which causes the "rear abs" light to come on and stay on until the ignition switch is turned off. The "rear abs" light comes on at the same time that the speedometer drops to 0 and the transmission seems to disengage (like it is in neutral). The problem only lasts a few seconds at low speed when cold so far. The light will also come on about 20 seconds after starting while in park. The brakes seem to be ok and the brake fluid level is normal. I looked at the connectors for the brake fluid level switch, the speed pick-up on the differential and the abs module under the van, all look ok. If anyone has any ideas of the problem I will appreciate the help.

Thanks,
Glenn

 

>I have an intermitent problem which
>causes the "rear abs" light
>to come on and stay
>on until the ignition switch
>is turned off. The
>"rear abs" light comes on
>at the same time that
>the speedometer drops to 0
>and the transmission seems to
>disengage (like it is in
>neutral). The problem only
>lasts a few seconds at
>low speed when cold so
>far. The light will
>also come on about 20
>seconds after starting while in
>park. The brakes seem
>to be ok and the
>brake fluid level is normal.
> I looked at the
>connectors for the brake fluid
>level switch, the speed pick-up
>on the differential and the
>abs module under the van,
>all look ok. If
>anyone has any ideas of
>the problem I will appreciate
>the help.
>
>Thanks,
> Glenn


all I can tell you is to undo all the abs connections and blow into the conecters and put them back to gether make sure they
click

 

 

Hmmm, it is possible that your speed sensor is going bad. Since you mentioned that the speedo goes to 0 then the ABS light comes on, that would be my guess. This has happened to me on a 94 F250. My symptoms were that the ABS would come on after maybe half a minute of idling. The speedo would occasionally fluctuate and over time as it got worse it would drop to 0 and it would kick off the Cruise control. While reading A Haynes manual and I even think it is mentioned in the owners manual, the only thing that usually affects all three, speedo, cruise and ABS, is the speedo sensor. You will still have brakes in a "limp home" mode, ie they will work fine but without ABS functions, which you almost never use anyway.

The Speedo sensor is a walnut sized thing that sits kind of on the top front of the differential, at least on an F250. If I recall correctly it is the only thing with wires in it that is sitting on top of the diff. Very easy to replace and I think it costs less than $30. The dealer will charge you a lot more to do it, this is easier than changing your oil.

If the gear on the sensor is chewed up you probably should also do a differntial oil change.

Good Luck,

Jim Henderson

 

You will see metal flakes on the sensor, which will indicate something is chewing up if the diff. I have the exact same thing going on in my 95 F-150. Already replaced sensor (which was $12 CDN, from Ford dealer), but it did it again later on that day.
I am not going to touch it til I switch my 3:55's for 4:11's. It's been over a year, and I haven't been caught for speeding yet (in my truck anyway).

Les