No Rear axle sensor signal

[Cobraguy]

Can someone please offer some insight here? 99 5.0 Eddie Bauer. I have an ABS light. Two codes...one for the RF sensor and one for the Rear sensor. Throw the scan tool on for live data, and sure enough, those two show no speed when moving. LF is fine. Dealing with the rear sensor now...how can this be?? How can this show no speed, yet everything else on the vehicle works fine that needs a VSS? Speedo, trans, everything. This is the same sensor that the VSS is generated from, correct? According to my manuals and diagrams, the rear sensor signal is sent directly to the ABS module, then distributed to the rest of the car. So if the rest of the car has a signal, how can the ABS module not?? Bad module maybe? Hope not...those are really spendy...

 

[ExploringNC]

The sensor for the rear ABS is on top of the gear housing. Take it out and clean it off, over time it will biuld up small metal shavings from the gears. Not saying that is the problem just something to try.

 

[Cobraguy]

Remember though...it's working. The ECM, cruise, everything but the ABS is getting the signal. The only thing that isn't is the ABS.

 

[gijoecam]

The ABS relies on all three sensors to function properly, but the system is smart enough to know that if it's getting a speed reading from any one of the three, and the other two are out of range, that must be the vehicle's speed. In fact, if you want to try an experiment, I'd bet that if you unplug the left front speed sensor (on the frame rail in the wheel well), your speedo would croak, shifting would default, CEL would come on, and cruise wouldn't engage. My understanding is that basically the system relies on a composite of the three sensors, and if one or two of them are out of whack, it doesn't necessarily mean everything takes a dive.

And you are correct, the ABS control module does monitor the sensors, then output the signal to the other components... PCM, ECU, stereo (for the Speed Volume Control), Lamp Out Module, instrument cluster, et. al.

-Joe