Well, after finally overcoming my blown headgasket issue with Superblue (thanks not to Blue Devil "Pour and Go" but to Bar's Leak's "Head Gasket Fix"), my '94 4.0, she is now giving me ABS fits. Both the ABS and BRAKE warning lights are now on. Also, I do NOT hear the ABS pump priming up from time to time, like it should. I did check both 30 amp fuses for the ABS system (i.e. one for the pump and the other for another part of the system) behind the knee bolsters and they are both fine. I also checked the ABS ECU in the boot and tried disconnecting and reconnecting it, in case it had somehow developed a loose connection. Finally, I pulled the (yellow) ABS relay from behind the passenger side knee bolster, cleaned the connections up and replaced it. I did all this in the parking lot of a WM a couple of nights ago. Strange thing is when I returned to Superblue after shopping and started her up, her brakes were working normally again, yet both the warning lights remained on. (I didn’t happen to notice whether the pump was making its usual sound, though). By the time I made it to the far side of the parking lot, however, the brakes were a no go again (and the warning lights still remaining on). I would like to know how to test the ABS relay, being that it is the only yellow one on the XJS and cannot be swapped out with another similar one. This one appears like it might be the factory original, and has the leaper emblem on it (along with a warning that it should only be replaced with another Jaguar factory unit). ? Same for the other relay for the ABS system, the white one in the boot next to the ABS control module.

Assuming that the ABS relays turn out to be O.K., any idea what the problem could be? Hopefully it’s not the ABS pump/accumulator/combo pressure switch assembly itself (which still looks to be pristine after all these years, btw), as I have heard good use ones are “very unobtainable” and $$ whenever one is located. Actually, I don't suspect the accumulator (although I have never had the need to replace one come up in any of my Jags) as it is my understanding they usually go out slowly and give some "warning" before finally giving up the ghost, such as the ABS light coming on whenever the brake pedal is pressed, or at least from time to time. I didn't have any of that before now.

 

AttyDallas,

Before you start examining components, just do the Blink Test to see what fault codes it has thrown which are causing the lights to illiuminate. Then depending on the results of that, do the 32 Continuity tests if it is relating to one of the electrical components.

Good luck

Paul

 

Thanks, but you've totally lost me. "blink test"? My '94 only has the JDS, and there are no diagnostic trouble codes in it for the braking system (only a total of less than 20 codes available?). The JDS, FWIW, is continuing to show FF44 on the screen, for a (supposedly) bad heated O2 sensor, as it has for well over a year now. So wish she WAS like Superblack, my '95 4.0 (R.I.P.) .. I really miss her OBD II system.

And, what is the "32 continuity" test?

I was thinking of making a list of all the ABS system components here, and ask in which order (and how) I should test them (based on ease or greatest likelihood of being the culprit). In fact, while I'm at it,

1- yellow ABS pump relay (behind knee bolster)
2- white ABS system relay (left side of boot, next to the ABS module)
3- the ABS module itself
4- accumulator sphere (AFAIK, never replaced .. had someone tell me recently they go bad @ about 10 years, due to the internal rubber "bladder" wearing out - I have never had an accumulator actually go bad in any of my previous Jags, btw).
5- combination switch (blue)
6. "anti-skid" controller
7. ABS pump

Given that I'm not hearing the pump doing anything, I suspect itself may be the culprit. Can 12 volts be applied in situ to it, and it should just run if good?

I also wonder if there is a big clue that I did, FWIW (given the warning lights are already on) I did the "14 brake pedal pump" test on her, not long before I started her up in the WM parking lot that time she drove across it w. the ABS working again (although the lights were still on). Could I have manually built up pressure sufficient in the system to cause that, albeit only for the journey across the parking lot, despite the fact the lights didn't go out? If so, I'm thinking that means again the pump is bad. ? I guess I could try doing that again and see what happens.

 

AttyDallas,

I've never heard of the "14 brake pedal pump" test? Where did you read about that? You can't manually build pressure in the system, pressing the pedal. All you can do if you press the pedal when the ignition is off. is dissipate the boost pressure. That's why we recommend that you would fully dissipate the accumulated pressure by pressing the pedal 25+ times before testing the pump or changing the accumulator sphere etc.

If you PM me your email address, I'll send you the Blink Test documentation and the Continuity Tests. I'd really recommend you do those first before trying to do anything else.

Cheers

Paul

 

The 14-press test I think is mentioned in the Jaguary factory workshop literature, or perhaps in a T.S.B. I thought it was pretty well known among Jag owners (or at least XJS owners). With the key off or in pos. #1 (IIRC, the latter, but can't recall at the moment) you should be able to apply the brake pedal at least 14 times before the brake warning light comes on. If it comes on before then, it is a sign the accumulator is not up to par (and the sooner the light comes on the worse condition the accumulator). I think I have stated how that procedure works correctly.

Will PM you my email addy, and thanks.

 

Out of curiosity, did the brakes fail completely or just a lack of power assist?

 

Just the power assist. From my understanding of the Teves III brake system, when the ABS fails then there is NO brake pressure applied to the rear brakes, and no assist to any of them, leaving just the non-assisted front brakes to stop the car. No wonder why it is a bit "challenging" .. Thankfully I still have a pretty good set of front pads on her ..

 

It's the Teves Mk II system that is fitted to 88-95 XJSs. If the ABS fails and / or is turned off by the ECM, then boosted brakes are maintained for all four wheels. However, if the boost pressure circuitry fails, then only the front brakes remain, in unboosted form.

Hope that clarifies things

Paul