Hi folks, another ABS query.


On pages 104 & 105 of the 4.0 supplement of my XJS service manual is a list of what all 28 connectors to the ABS control module do. On pages 108 & 109 various tests are listed for checking voltage, resistance and continuity between single or combinations of connections to check for faults.


My 1990, 3.6 has 35 connections to the ABS control module, although 6 are blanks. Does anyone have or know where to find the equivalent list as to what they all do / how to test? I worked out from a wiring diagram which pairs serve each wheel sensor and the resistances are all similar and within specified tolerances so would like to test the rest to try and find out why my ABS warning light is on all the time.


Thanks for reading,


LeeP

 

Hi Lee

Maybe the ABS Fuse has Blown? its located under a Cover under the knee pad on the Passenger Side of the Car.

If that Fuse has Blown the ABS light will stay on.

Or it could be a loose or dirty connection on one of the Electric Plugs on the ABS Master Cylinder/Actuator.

 

Thanks orangeblossom but fuse seems Ok. Have now tested all the terminals in the connector that fits into the ecu for power and earth continuity with ignition on and off.


At least the terminals that serve all 4 wheel sensors give similar resistances and within service manual tolerances so presuming they are ok.


About to sit down with a glass of red to study the wiring diagram and see if I can figure anything out.


Cheers,


LeeP

 

Hi Lee

There is always an outside chance that one of the Valves in the ABS Master Cylinder/Actuator may be malfunctioning or blocked.

Which 'Could Possibly' cause the ABS light to stay on but since its an easy test to do, you may as well give it a go.

With Thanks to Rennsport.

RennsportKC ? Jaguar XJS ATE ABS repair?

 

There are 3 level switches in the reservoir the first 2 will turn on the Brake Failure warning if the fluid drops lower there is another switch that turns on the ABS light. Check this switch is NC check this is not open circuit, a broken wire could cause this.

The ECU will also turn on the ABS warning if the pressure is too low, does the pump run for about 20-30 seconds when you turn the ignition on?

The ABS light indicates failure of the ABS system, this deactivates the ABS and braking is only available on the front wheels.

Pin 3 and 20 on the ABS ECU should have 12v with the ignition on.

Wheel senors will cause the ECU turn on the ABS warning light so check these for damage including the wiring.

edited for faulty user

 

Thanks Orangeblossom (and also to Rennsport) that was a really useful link. Now for the bad news....


I have resistances of 5.9, 3.6, 3.6, 6.0, 3.7 and 5.9 ohms and so based on the link I presume that means I have 3 duff solenoids in my ABS valve block. Haven't worked out yet what my options are i.e., strip down or find another unit so any suggestions to that effect much appreciated.


Cheers,


LeeP

 

Hi Lee

Although I've rebuilt a Couple of these, success is not guaranteed, because until you take the unit apart you won't really know the Condition of the Valves.

So it 'may' be best to get one that is working from a 'Scrap Car' as at least you now know how to test it.

And then rebuild your old unit at your leisure, as although its fairly easy to do, you have to be very meticulous when you rebuild it.