Hi all! I’ve struggled with this, and ask around for years, but nothing seems to help that’s suggested. I have both an ABS and a speedometer issue.
The ABS light is on, and when I hit the brakes, the brake light on the dash comes on. Let off, it goes off too. When I hit the onboard diagnotic, “PAD” comes up, again a braking issue. The speedometer doesn’t work either (never has since buying). I’ve replaced the speed sensor (right front wheel), the ABS computer (3 times to be sure, left side in trunk), and the 2 relays under the driver’s side dash.
From my understanding, the speed sensor sends a signal to the ABS unit, which sends a signal to the speedometer.
Suggestions?
First, welcome to Jag-lovers! Great group of folks here, with a lot of collective knowledge and resources, so you are in a good place. Now, one issue at a time:
The PAD indicates either (a) one or more brake pads are worn to the point the in-pad sensor is contacting the rotor, or (b) there is a problem with the sensor(s) or the wiring thereto. On your 1994 model, the sensors are only in the left front and right rear pads, but they are wired in series (in a loop) so a problem with either one will trip the brake light and error code on the VCM. I don’t know whether you are adept (or even a novice) with wiring diagrams, but here is a link to the 1993/1994 updated electrical guide in my Dropbox account. Figure 13 shows the brake pad sensor input to the instrumentation:
Your understanding is correct in that all four wheel sensors provide input to the ABS ECU (in the trunk/boot), which in turn provides output to the speedometer in the instrument pack. The aformentioned figure 13 (instrumentation/warnings) and figure 25 (ABS system) in the electrical guide provide information about the communciation from the ABS wheel sensors to the ABS ECU to the instrument pack/speedometer.
Finally, here are three files that provide diagnostic information about the ABS system:
ABS Blink Lights.pdf (765.4 KB)
ABS Diagnostic.pdf (682.2 KB)
ABS Lights.pdf (182.6 KB)
There is a lot of information to digest here. Report back and let us know how you get on with it.
Thanks for the insight! I’ll look all this over and go from there
@Mike_Stone
Thanks for the info, really useful. 
@Dark Phoenix
Does the trip computer, or cruise control work?
It appears you have the Teves III brake system, which I assume is functioning and providing power brakes.
There is no internal circuit shown for the speedometer, but I’m pretty sure it will be a speedometer head with power and Gnd supplied from the board, then a trigger wire which is fed +5v from the speedometer, which the ABS Ecu pin 12 shunts to Gnd to register a single speed pulse.
The Ecu continuously shunts this open/closed to Gnd to create a digital speed pulse, the more pulses per second the faster the car is moving.
You can manually test this by firstly checking the output voltage is as I mention, then shunt the wire rapidly on/off to Gnd and watch the speedometer.
If the trip computer, or cruise control function then the problem is the actual speedometer…possibly dry solder joints.
You could use an Led to observe the speed signal.
The rest of the ABS system is pretty easy to diagnose using blink codes and a multi-meter.
There has been a fairly lengthy, eventually in depth, discussion about Teves III braking system and add on ABS.
The ABS is a separate system, with the only connection being the Main Valve, which is energised when the ABS is in use.
Teves iii braking system failure - XJ-S - Jag-lovers Forums