Hi, wonder if anyone can help me here with my 1990 XJS 3.6. The ABS pump/accumulator (non-vacuum-assisted model) isn't getting current - current is not getting to yellow ABS relay in passenger-side fusebox or the ABS fuses [which are fine, just no current]. Might somebody know where the wiring originates - wonder if it might go via the ABS ECU in the rear of the car or whether the pump/accumulator operates independently?

Also when I connect up the pump/accumulator to an external 12v source, it runs, but runs continuously (though I'll not let it run for more than a minute to avoid burning out the motor) and doesn't stop. Pedal goes from very hard to soft fairly quickly so I'm assuming the accumulator is working. Brakes have been bled and apart from this issue seem to be in order. And I've removed the pressure switch which from a visual inspection seems to be as new, no gunk or obvious damage.

Is driving me mad, any ideas most appreciated! Thanks, Nigel

 

Nigel,

Can you describe the symptoms a bit more? Is the problem that the pump doesn't run when you turn on the ignition? Do both of the brake lights extinguish? If so, after what time period? Is the problem linked or following any maintenance ie did you change pads or other parts? You mentioned that the brakes had been bled; why was this? Was something changed first?

Cheers

Paul

 

Hi Paul and thanks for your quick reply. Principal problem is that the pump doesn't run when I turn on the ignition. When I connect it directly to a battery booster it does run but doesn't turn off. Brakes were bled for general maintenance (not by myself) after adjustment of the handbrake which had only been working on one side, but I suspect this isn't linked to my current problem. No brake-related warning lights on dash at any time.

Cheers, Nigel

 

Hi Nigel

What makes you think the ABS Fuse is Ok?

Was it just a Visual Inspection or did you pull the Fuse out and then Check it?

You need to be absolutely sure that the ends of the Fuse are Clean and the same with the fuse holder.

Someone else had a problem like yours, which turned out to be a dirty Fuse rather than a Blown Fuse.

Can you expand on what you meant by someone else Bleeding the Brakes for General Maintenance.

Did they do this for a particular reason ie to change the Brake Fluid.

Something doesn't seem quite right with that.

If you Paid a Garage to do this, then I would be taking my Car straight back and getting them to fix the problem at their own expense, if everything was working Ok Before you took it in.

One of the reasons why I would rather walk on broken glass, before I let a Garage anywhere near my Car.

 

Nigel,

Apologies for asking what might seem like quite repetitive questions. Are you saying that no brake warning lights are coming on when you turn on the ignition? As I'm sure you know, the light should illuminate until the systems checks and pressure accumulation have been achieved. So did the light used to come on normally and then extinguish prior to the work being done? And has this now changed?

Try releasing the handbrake and turn ignition to Pos II. What brake lights are on? Then start the car. What brake lights extinguish or remain on?

There could be one of a number of reasons including a faulty pressure valve which is making the system think it's up to pressure from the outset. Depending how you're manually applying current, you could be over-riding the valve. But the absence of lights and their extinguishment concerns me. An ABS car must turn on the light and then extinguish it and I'm not sure if that's happening.

Paul

 

Hi and thanks again for your replies. Worryingly no brake lights turn on when ignition is turned to Pos II and handbrake released, suspect the previous owner may have been involved in some dodgy DIY for MOT purposes (I bought the car as a short-and-easy project last winter but has been off the road since MOT expired in May and the project become never-ending!). I can't remember whether this was still the case before booster stopped working.

The fuse is now getting current via the brown wire from the battery. Also the brown/orange wire from the fusebox to the yellow ABS pump relay is carrying current when the fuse is in place, but not when the fuse is removed. Ergo I'm assuming fuse and fusebox is ok, the fuses look new. However, despite receiving current, the relay isn't switching to send current along the brown/blue wire to the ABS pump.

Wondering now whether to directly re-wire from the relay to pump, and then re-earth from pump to ground (the brown/blue wiring to pump is hidden, think I might need to remove dash to investigate further, and have no idea where the ABS pump black wire earths to). And if that doesn't work, to invest in a new pressure switch which I think you're right could be one of the issues (though having removed it from the pump and examined it, it didn't have any obvious signs of damage and it is receiving current fine).

And @orangblossom, I didn't hire any garage, the brake-bleeding was done by a classic-knowledgable friend of mine (actually a JLR engineer), he's away on hols right now but I'll chase him for more info when he's back. I also avoid garages like the plague!

Cheers, Nigel

 

....and forgot to mention, I tested the ABS relay with an external 12V source and multimeter and it's working fine.

 

Hi Nigel,

The fact that the lights don't illuminate and your presumption that a PO may have done some undesirable things to the system would make me a little concerned. For example, has the whole ABS system been (worryingly) disabled at the ecu? I wouldn't want to be running the car without those lights working correctly as they are designed to illuminate if any part of the system fails and the ABS is thus disabled.

If it were me, I would start by fully reading the Brakes section in the Workshop Manual and also famiiarise yourself with the ABS wiring diagram. I would then check the electrical integrity and circuitry of the system by running the 32 electrical tests on the system as per the Workshop Manual. This will interrogate the electrical side of the pump, valve, ABS sensors, ABS valves etc. It's easy to follow and mainly involves back-probing the pins on the ABS ecu.

Good luck

Paul