Cruise control is managed by an computer up under the driver's footwell. When the cruise in my son's 95 940 failed, I performed the diagnostics thanks to the OBD unit under the hood. It returned "no signal from speedometer". The speedometer and odometer were working fine. I tested the output from the speedo using a multimeter and it "appeared" to be working. After making sure everything else was working, I finally replaced the speedometer and cruise returned to normal.
It so happens that the speedometer receives a sine wave signal from the rear axle sending unit and converts this into a square wave, with frequency proportional to rear wheel velocity, to serve as a the input into the cruise control computer. If this does not happen, no cruise control. I do not have an oscilloscope which would have made quick work of this diagnostic.
Anyway, if your cruise dies and you get this diagnostic report while your speedometer appears to be working fine, consider that the internal wave conversion might have failed. This means a replacement speedo.
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See the 700/900 "FAQ" at the menu bar top screen left side.