My 94 XJS was a bit different from what I experience in my XJ40 so I was hoping to get some insight. Every time I depress the brake pedal I can hear the ABS relay click and my lights dim for a fraction of a second. Is this normal or is there something I should service soon? Car brakes fine and no ABS light on. Thanks!

 

My 1991 4.0 does the same. ... waiting for responses to you....

 

DEAD ACCUMULATOR!!!!

bob

 

Ahhaa!

Thanks Motorman

 

thanks! If I get a second hand from a breaker, is there any precaution I should take other releasing the pressure? Any chance that one that had been sitting for a while have any chance of contaminating my system?

 

Since all of the original accumulator spheres are now several decades old, all of them are probably DEAD (lost the nitrogen charge).

I don't know if any are still manufactured. GM used the same system in some Buicks and Oldsmobiles.

You need to pump the brake pedal until your leg gets tired (KEY OFF) to ensure that there is NO RESIDUAL PRESSURE in the sphere. Unscrew it and replace the accumulator.

Plenty of info on accumulator sphere replacement on the forum.

bob

 

gotcha. I tested my system by letting the pump do its thing with the ignition in the second position. Then i turned the switch back to shut off position. I then pumped the brakes and noticed that it isn't til the 23rd pump that the pedal got noticeably firmer. I then restarted the car and the ABS light flashed for a few seconds while the system recharged the pressure. Light came off. i got a quote for an accumulator at $500 ouch! Any better sources?

 

okay Im getting ready to buy one asap. Just want to confirm that everything Ive listed in my previous posts is truly a bad accumulator. Thanks!

 

Sounds to me that the accumulator is fine, but I'm not a brake expert by a long shot! - OTOH, if this were my car, I don't think I'd swap the accumulator if it took 23 pumps to firm up?


The lights dimming? bad connection somewhere?

Larry

 

yes the lights dim a bit when the relay clicks and then brighten back up to normal. I do wonder what it could be then....

 

Not sure!

However, Don's favourite process is cleaning all the grounds, and that's a good idea whether things are ok at present or not! These cars are 50% electrical after all!

Lots of info on that in the archive, he also has a photo album on the locations - my favourite electrical cure-all is the reflowing of the solder joints in the fuseboxes but in this case I think the grounds win out.

Like I said, worth doing anyway.

Larry

 

Hi Brewtech,

Please add your XJ40's year, model and engine info to your signature line so we don't have to ask or try to find it in your other threads. This is important because, for example, depending on the year of your car the GM/ACDelco/Buick Reatta accumulator may fit or it may not; the number of ABS relays may be three or two; etc.

Which leads to the question, which of your ABS relays is clicking and where is it located?

Which lights are dimming? Instrument cluster? Interior overhead lights? Headlamps?

P.S. Jagbro, please add your Jag's year, model and engine to your signature line too....

Thanks!

Don

 

Ya know I added it to my sig, but i haven't seen it pop up... I'll try it again.
Yeah its my Headlamps that kinda dim and go back to normal for the 1 sec when I hear the relay behind the instrument panel

 

The dimming headlamps have to be a clue to something, though it may not be part of your ABS issue.

It might be worth having a basic free battery and charging system check at a local auto parts store. It's possible the voltage regulator in the alternator is not regulating properly. After the initial test, try pressing the brake pedal while a second test is being run to see if it indicates a problem like a significant voltage sag.

A '94 XJ40 has two ABS relays below the instrument cluster. One is the ABS Main relay, and the other is the ABS Pump relay. I'm falling asleep so I won't attempt to interpret the operation of those relays, but I think the ABS Main relay should be on any time the key is in the ON position. The ABS Pump relay should be activated only when the combined pressure switch on the ABS electrical pump opens, activating the relay and powering the pump.

So it seems like it has to be the pump relay that is clicking when you press the brake pedal because the system believes the pressure is low. Do you hear the electric pump on the right firewall run when this happens?

Cheers,

Don

 

ok, I'm editing my post. In Park, Im hearing a click when I depress the brake pedal, at the shifter, which is probably a shifter lock, and then I hear a less audible click behind the cluster. My wife depressed the brake pedal for me while I had my ear to the ABS pump and yes, it does run for couple of seconds when the pedal is depressed. I take it this is not suppose to be happening every time I use the brakes, the system should hold pressure for more uses of the brakes. After shutting the car off I pumped the brakes again and noticed that the pedal got firmer around the 19th pump. Starting to think the accumulator is packing its bags. Should I order the JLM1907 for this specific car?

 

I haven't looked up the spec in years but 19 pumps strikes me as perfectly serviceable. The fact that your car brakes fine and you have no ABS warning lamp illumination makes me more inclined to suspect that the half of the combined pressure switch that controls the pump relay and pump may be malfunctioning or there may be a problem with its circuit.

I'm attaching the Power Hydraulic System Manual which has some diagnostic flow charts that may help you track this down.

I'm still concerned about the fact that your headlamps dim when this happens - that indicates a significant current drain somewhere, and the voltage regulator should be able to compensate for that.

Cheers,

Don

 

Im going to try to clean the pressure switch. Same procedure? Relieve the pressure from the system and then removed the switch?

 

I don't know that there is much you could accomplish by trying to clean the pressure-sensing end of the switch, and based on your symptoms, it seems like that end of the switch is working because otherwise you would have the ABS or BRAKE warning lamp illuminated. The switch is like something from a nuclear submarine, so before removing it I would suggest testing it electrically at its integral connector. Just refer to the schematic in the Electrical Guide to see if the two pairs of terminals should be open or closed at low or high pressure. Off the top of my head, I think the contacts are open at low pressure.

You could certainly clean the electrical connectors on the switch and its harness and check that the connector is seating fully and latching properly.

Did you not find a diagnostic flow chart in the Hydraulic manual that might help?

Cheers,

Don

 

Yes. Started reading it this morning and will see how it goes. My car is a 1994 so the 1988-89MY makes me think I have to just apply it to my car

 

Have a look at jagrepair.com, you'll find plenty of info there.