XJ81 with no ABS or Brake warning lights on but speedo does not function

Hello All:
I recently acquired an early 1994 XJ12 or XJ81 car and I am slightly puzzled by some issues with the car. The speedo does not work at all. I had the same problem in my 1994 XJ40 car and I had to replace the ABS wheel speed sensor located in the hub for the left rear tire. This fix worked in that MY94 XJ6 car but when the speedo was not functioning due to the lack of a ABS signal from that wheel, there definitely was a ABS warning lamp illuminated on the dash. Since I replaced the sensor in the hub carrier for the left rear wheel in my 1994 XJ6 car, the speedo and odo have worked fine.

I am puzzled by the non-working speedo in the early 1994 XJ81 V12 car since no ABS warning light is illuminated on the dash. I would expect if that left rear wheel sensor was not functioning that a ABS warning light should be illuminated on the dash. Is that true or not?

I just went out and checked that ABS wheel speed sensor with an ohm meter and it is indeed an open circuit so I do believe it is bad but if that is the case why is the ABS warning lamp not illuminated on the dash? Even when I use the brakes I do not have any ABS or Brake warning lamps illuminated. Comments, advice, or info about this most appreciated.

I do notice another questionable thing with this car. When I turn the key to the ON position (not the start position) and hit the VCM button on the dash, absolutely nothing happens. No codes are shown at all. The display just goes blank for a few seconds and then immediately goes back to displaying the odometer reading. I don’t know if this is normal or not since I have never had a car that had zero codes showing. Can anyone else tell me if when pressing the VCM button if this blank display and then immediate return to the odo reading is normal or not?

This is normal behaviour. At least this is the way my 94MY works.

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