I have a 1993 xjs with the teves iii braking system. The brake pedal goes to the floor whether engine is running or not, and it slowly returns. The brakes grab initially but eventually let go as the pedal gets lower and lower. I’ve checked all brake lines and there is no leak from the system anywhere. I’ve replaced the master cylinder complete unit with reservoir and filled with fresh dot 4. The issue is exactly the same after the replacement. I have both brake and abs warning lights on. The only time I heard the accumulator running was after the replacement cylinder was installed initially. If I pump the pedal I can hear the brake fluid circulating in the reservoir whether engine running or not. It’s as if the fluid is simply returning to the reservoir and the system never seems to have pressure in it. I’ve checked the main abs relay and can confirm it’s functioning. Could this issue be caused by a failed accumulator or failed ABS module? or even as a symptom of a failed pressure switch? any help appreciated.
You may have several troubles, including failed accumulator, BUT 1st- get your pump running! It MUSt run, and the “red lite” to cycle off when up to pressure. That is true even with failed (trunk mount) brain, et cetera. Over cycling and all= bad accumulators, but #1- try to get pump to run. Best luck, + more specifics = chance at best help. I’d start at pump fuses, connections , and relay.
Steven,
What us the history of this car? Was it running nicely and the brakes working properly for you and then the ABS problems recently started? Or did you recently acquire this car and you are trying to sort out the ABS problems that someone else either couldn’t or didn’t fix?
Paul
Hi Paul, yeh I bought the car with the fault and I’m trying to resolve. As far as I know the previous owner didn’t even attempt to fix it, he was driving and the brakes went suddenly, that’s all I know. I did note there was receipts for new rear calipers within the last year, and judging from the very little rust on the discs it appears the brakes had been working since the new parts. I read through some of your old posts which were helpful, as it sound’s like you had a similar issue with your wife’s xjs. Unfortunately I’ve not found the smoking gun as yet, I’ve ordered the service manual and have a list of diags to try on the ABS. I’m just muddling through, so thought I’d reach out for some more experienced advice. This is my first xjs and my 3rd classic car, hopefully I can get her fixed as I’m planning to keep her, I’ve been after a good one for years and this showed up in the spec and colour I was looking for.
Steven,
Did you download Kirby Palm’s “Experience in a Book” from Jag-Lovers and review the section on ABS?
My wife’s 1990 XJ-S convertible (5.3 L V12) had an amber ABS light which I fixed by replacing the accumulator ball, and then a red BRAKE light that I fixed by replacing the Combined Pressure Switch. We still have that car and the ABS continues to work properly. AFAIK the ABS pump always worked properly in our car but it seems like the pump is not working in your car (1993 4.0). As jp2 pointed out you need to get your ABS pump working properly.
I also found the ABS section in the Jaguar Repair Operations Manual (ROM) helpful when I was sorting out our ABS issues.
Paul
Thanks Paul, I’ll take a look at the book you suggest, as for the manual it’s on it’s way as I couldn’t see it online. As for my issue, the only time I heard the pump firing up was just after I replaced the cylinder, which I took as a good sign, but it’s not run since. I did notice something else, which I’ve just remembered, the ABS relay at the dash was hot to the touch, I haven’t checked this as yet, is this normal? I was also under the impression if the ABS pump / module fails then I should still have working front brakes, is this not the case?
Plan on pin by pin testing. M Cyl float, Press switch- by acc ball, then at computer if reqd.- left trunk. But first keep M Cylinder level high, assuming all stock set up. Foat doesn’t jive with Full Level mark in plastic. After you get pump running, be critical on the acc ball as the pumps are dear. Best to reduce run time. The balls are out there- check old posts, or source a GM spare.
Thanks both, I’ve made some progress today, traced the pump not running back to bad abs relay under the dash, fixed and now pump is running again and both brake warning and ABS lights have gone out. Strange thing is pedal is still going to the floor, except each time I press it the pump runs every time, for only a couple of seconds. Checked all the brake lines again and still see no leaks. The fluid level dropped a little when the pump was charging as expected but plenty of fluid in reservoir. When I press the pedal reservoir drops a little then pump runs and reservoir tops up again…
Lucky guy! When in doubt- just blead. Rear system instructions are a bit queer, I’d do fronts first-normally- but I think you said they worked on rear- there ya go! Dot 4 is cheaper than parts- so don’t be stingy, and you dodged a bullet.
Indeed! 
I’ll give them a good bleed at the weekend. I took it for a short drive this evening and it was pulling to the right on braking. I’m hoping a good bleed should help this. Thanks for your advice. Much appreciated to you both.
Update: Brakes now working again after a long bleed, couldn’t believe the amount of air in the system… So in the end bad ABS relay and air was the cause of the failure.
Steven,
Congratulations on getting your brakes working again properly. Often it is the obvious things that are the cause, and not some obscure failure, as you found with the failed relay and air in the brake lines. Great job troubleshooting and finding the problem instead of just throwing a bunch of expensive replacement parts and hoping for the best.
Thank you for posting back with what fixed your ABS brake problem because that adds to the collective knowledge.
Paul
Not wishing to appear pedantic, but there is no ABS pump fitted to the Teves III system…which is why it has to have the power brake system.
You did a great job, correctly advising the O/p to KISS (keep it simple) and get the brake pump running, as no pressure = no rear brakes or assistance.
Please see other thread which includes the operation of the brake actuation unit and a description of it’s function and failure modes.
The ABS is a simple add on. The Ecu detects wheel locking so opens the actuation unit main valve and operates the respective wheel solenoid valves while the main pressure pump keeps supplying fluid at pressure.
Brake Booster failure - XJ-S - Jag-lovers Forums
p.s. I love reading about proper diagnostics revealing a fix without any parts required, or only the actual faulty part was replaced.
Oh Boy- At a disadvantage as I ain’t an English teacher. Lets see- Teves III is, by definition, and/or patent, is an anti-lock (3 Channel) brake system. For the ABS to function it incorporates- 1) A pump to pre-charge the system, and 2) an accumulator to hold the pressure (energy) within a modest volume of fluid to be at the ready- at all times, save perhaps, at initial cold start up. BUT the required Pump in the ABS system is not an ABS pump !??!. So a “Main Pressure Pump” used to make the installed ABS system “Mainly” work is now not “mainly” an ABS pump , yet owes its fitting solely to the fitment of the ABS system. Do I have it? If so : woe’s now mainly on first???
Strange in that is similar to most of the symptoms I’m having with Superblue’s ABS system. Only thing is that the pedal is HARD, and when the car starts the pump never energizes (and I don’t hear it running at any other time). So, my thinking now is the culprit is simply a bad pump. Is there a quick way to test it in place, using 12 V source (although I notice on the top of the housing it says “13 V” … wth?). 
How did you find out the ABS relay was bad? I need to test mine (both the yellow one behind the bolster and the white one in the boot) … Problem is they are unique and there are no other relays to swap them out with to see if they are bad … 
No ABS pump ??? then what is the black pump in the assembly for ?
Unfortunately you don’t “have it.” I’m not sure why you felt the need to be sarcastic, especially when you are wrong.
The pump is there to create a fully pressurised brake system…power brakes.
The rear brakes are powered soley by the pump, there is no master cylinder to generate the pressure.
As already said, the ABS is an add on Ecu and valve block and has no integral pump as it uses the power brakes pump to supply the pressurised fluid.
While ABS is in use both the front and rear brakes are fed directly from the high pressure pump, whereas in normal braking only the rear is fed by the pump and the front fed by a master cylinder.
As the braking system is powered, this creates an advantage for bleeding both rear and front circuits.
Turn on the ignition to charge the brake system, prop the brake pedal down to open the control valve then open the rear bleed nipples to bleed the rear brakes.
For the front brakes instead of performing a manual bleed you could simply energise the main valve by shunting power to it, then perform the same power bleed you did on the rear brakes.
This way you have bled the brakes and tested that the main valve functions.
Thinking of the Teves III as a standard brake system with pressurised ABS is why people are confused, it is a pressurised brake system with an add on ABS valve block, without a pump.
Without the pressurised fluid the rear brakes don’t work at all and there is no assistance for the front brakes, hence the hard pedal.
I’ll post the link to the relevant thread again, as it appears to have been not seen in my previous post in this topic. The information you need is there. 
Brake Booster failure - XJ-S - Jag-lovers Forums
To whet your appetite for the juicy information you are about to discover, here’s a system diagram. Note the first part after the reservoir is the pump. There is no pump in the ABS valve block.
Your failure is almost certainly the relay has a poor connection, same as the O/p in this thread. Normally, relays burn out before pumps.
A 12v test lamp is all you need to diagnose this.
I carefully opened the relay and inspected it, it looked like water had got to it at some point as it had a small build up of rust, I cleaned it out and lightly sanded the small electrical contacts in it then reconnected and found it worked after pumping the pedal a few times…
Flashback time- Decades ago was trying to stay awake during “capacitor” day in class. Kid in the back got most upset when he figured that the millions of cars (tractors, et cetera) that were built with so called “Condensers” to stop the burning of their contact points really had Capacitors. No feed back to report regarding his massive recall campaign. What do I call the pump on my Cadilliac? The parts man calls it “Power Steering…”. Used in a sentence… “Here sir is the Power Steering belt you wanted…”. G. M. MAY call it Hydra-Boost. The pump also provides power break boost. If I turn into the parts store, THEN stop must I request a ‘Break Belt’ ??