Hi Simon

Please let us know when you've got it fixed, as your ABS appears to have a problem that is proving quite difficult to resolve.

 

Hi Simon,


The 12V supply to pin 2 comes directly from the ignition switch. There is nothing in the braking system either ABS or conventional that could interrupt this supply. If you don't have 12 V at pin 2 (with the ignition on) it is either the ignition switch or the wiring between it and the ECU in the boot that is at fault.


It is also worth checking that you get 12 V on pin 19 when you crank the engine. This is the warning light bulb check facility and another check on the ignition switch / wiring between it and ECU.


I am not aware that the 32 diagnostic checks are year specific and so the function of the 35 pins should be the same for all model years but others may be able to correct me on this.


You asked earlier about which pins on the ABS ECU are in use. On my '90 3.6 all 35 pins are used except for:

• 13, 21
• 28 to 31 incl

Remember that as you look into the connector from the wiring loom, with the locating hook at the bottom, pins 1 to 18 are on the right and 19 to 35 on the left. So pin 1 is top right hand side.


I can see no other course of action but to check for 12 V at the various terminals and connectors from the ignition switch back to the ECU. A pain I know. There is, I believe, a block connector under the centre consol / storage box that might be worth a look if you are not getting 12 V output from the ignition switch.


I wondered if there was a way of somehow hot wiring a 12 V supply physically into the connector between it and ECU to feed pin 2 purely as check to see if your warning light extinguishes (you may have to drive to clear fault - find a quiet road). Not sure how practical this is and you would need a very thin wire.


Good luck,


Lee

 

Hi Guys,

So a bit of very interesting information has come to light RE my electrical test on the ABS system... I am an idiot.

I was looking at the diagram on the ECU tell me which way the pins were number, but obviously thats for the ECU the connector needs the reflection of that ! So effectively all my previous tests were bobbins.

I have now gone through most of the 32 step diagnostic process and have what appear to be some more meaningful results.

All the of the test pass bar 4 and the additional 4 I didn't try. The tests that failed were the continuity tests to all four wheel sensors. I did bother with the four voltage tests for the wheel sensor because it sounded like a lot of work and didnt have an assistant to spin the wheels themselves. I couldn't see them passing with the continuity tests failing anyway.

As I'm reading it, that basically saying all four wheel sensors are either unpluged or goosed. Given the only work I've really done is on the front wheels, it would seem extra-ordinary for all four wheel sensors to go pop at the same time. So what I'm hoping is someone is going to tell me there is a massive plug somewhere that they're all connected through that I've somehow unpluged....please... anyone...

Failing that, can anyone think of way they can all get unpluged once, given their respective locations I find it difficult to believe they're all plugged in at the same spot bar the ECU so I'm hoping something else could account for their failure.

I'm thinking the first step would be to disconnect one of the sensor and jump it's wires see if that gives me continuity at the ECU. That would tell me if the wiring to that individual sensor is sound or not. I guess the wiring to the in sensors is fine I'm going to have to spring for 4 new sensors.

Any thoughts - other than I'm an idiot for the plug-pin swapping :-p

 

Hi Simon,


Don't be too hard on yourself re the pin confusion. There is no guidance on this in any of the manuals and it took me a lot of head scratching to think it through.


Like you I find it hard to imagine how all 4 wheel sensors would shut down at the same time. So a test on wiring continuity (from each sensor to the relevant pins) is a good start. I think there may be some inline connectors within a foot or so of each sensor so this may be a good test location. If this pans out I can only assume that you have all 4 wheel sensors failing in harmony (still seems unlikely) or the ECU has packed up.


I rigged up some test inputs to prove my ECU was ok on the basic inputs but input from the wheel sensors would be far more complex. The simplest check would be to find a friendly nearby XJS owner with a working ECU and no ABS faults and do a temporary swap to see what happens.


I'm away for a week or so and may not have emails so let us know how it works out.


Good luck,
LeeP

 

Hi leeP, it was actually your post that got me thinking. I got about half way through your sentence and I was like 'hang-on'.... so many thanks just for that, all told Id be willing to be that going to be the biggest barrier...

I guess we're both agreed the next step is checking the wiring. I can't see them all failing.

I noticed you questioned the Ecu itself but I'm kinda of the opinion that it's receiving signals jaguar isn't expecting - by their own diagnostic sheet - so at the moment I guess I'm happy to say the ecu is off the table till I can verify that the signals it's getting are correct, indications so far are that it is isn't getting the right information for whatever reason. So I want to correct that before I step on.

Next point as far as I'm concerned is getting every sensor to pass every jag test. Not quite sure how I progress that but it is my plan..

But ultimately I'm a lot further on than I was with my mis-test so thanks a whole bunch for getting me passed my ineptitude...


Simon

 

Hi Simon,
You are correct re the ecu being off the agenda for the moment. I was talking nonsense last night because (thinking again) the problem seems to be upstream of the ecu somewhere between the connector and the wheel sensors.


One minor point; the Jag wheel sensor test refers to resistance between pins 6 & 24 etc. not continuity. Are you saying that there was no continuity between the respective pins so you could not measure a resistance?


Also I'm puzzled why your "warning light flash test" did not point to wheel sensors.


Next step would be to disconnect the sensor at the wire connection and check the sensor for resistance and the wiring for continuity.


Good luck,


Lee

 

Hi LeeP,

My multi-meter doesn't seem to differentiate between a continuity test and a resistance test, i.e. very low resistance is continuity. I'm not super good at electrical stuff but I put the meter in what i think is the right mode - If i hold the probes apart I get "1" if i touch them I get a something like "0.004".

Each time I put the probes on the respective pins I got "1", which I'm assuming means the signal the meter is sending isn't returning at all. So I took that as no continuity / 100% resistance.

Might sound a bit noddy but given my earlier mistake I'm just wanted to check I'm not doing something (else) stupid.

My plan is to find a connector in one of the wheel sensors, jump that with a paperclip or something and see if I can get continuity. That would tell me the wiring to at least that connector is good. If it is I'm guessing doing the resistance test from the other part of that connector directly to the sensor is just as valid so that would tell me if it really is the sensor or not.

Fingers crossed it's something between the ECU and the sensors wiring cos I just can't imagine all four sensor going. If it was just the front I'd even be open to saying I'd mucked something up but like I say I've not even touched the rears. I also can't really see how if one sensor was super-broken it'd stop the others having continuity/resistance.

Still I have a next step, hopefully that shed some light...

 

Simon,


It sounds a plan but If I were you I would first get hold of a multimeter that can actually read the resistance. The requirement is pretty high at 0.8 to 1.4 k ohms. My own varied 1.07 to 1.12 k ohms measured at the ecu connector.


I will probably be off line for the next couple of weeks so good luck.


Lee

 

Maybe a stupid question, but when you first start the XJS, how long should the brake/ABS light stay on? 5-10 seconds? Does it go off right away? Just curious if it is on long, it may show that an issue is arising. I am assuming that it is building pressure within the system and then the light switches off.


I hope you work out your issue. Thanks..

 

Perhaps I had the meter in too higher range, i'm not totally sure I checked that to be fair.

 

Just to let everyone know where I am with this. I put the multimeter in the right range and got sensible around 1100 off all but one of my sensor - the front right where all the work had been done due to snapped bolt.

I got a secondhand part off ebay and measured that before attempting fitting and it was giving decent results too. When I went to take the old one off, the back with the wires attached totally separated from the rest of the sensor with the slightest touch. I checked the wires for continuity with the plug in the under the bonnet and they were fine. So I concluded that it was extremely likely the sensor itself had failed, or just been disconnected but it didnt seem to want to go back together.

I went to fit the new second hand part but the seller had sent me the left hand sensor, the wiring exits the sensor facing the wrong way and wont clear the shock. I got back to the sell and he apologized and said he'd send the RHS one immediately. The RHS sensor arrived and the wring insulating rubber was much more perished on this one - you could see the magnetic shielding at several points. I multi-metered it before I even started and it was dead. So I didn't even attempt to fit.

Now i have two RHS that don't work and a working LHS !

I've ordered a new-new part from different supplier, I'm fairly confident when that gets here and fitted my ABS problem will be resolved - everything was fine before the hub work on that wheel.

I was waiting to update with a full success story but the delay in getting parts etc has meant the thread looks abandoned without resolution so i thought I'd update.

 

Hi Simon,


Glad to hear you seem to be approaching a fix and thanks for keeping us all posted.


Sorry to hear you are receiving some duff parts from the second hand trade. Would be interested to hear who you have had problems with - drop me a PM if you like.


Cheers,


LeeP

 

And so it continues... but I have made significant progress.

I've bought a brand new ABS sensor for my car, right year and everything. The new sensor is made by bosch. It returned the correct signals on a bench so i went ahead and fitted it. The sensor itself is a slightly different shape etc so I was bit concern when I couldn't get it in the gap at the hub past the shock. Lowering the car back down onto its wheels altered the geometry slightly and it eventually slotted in.

I ran the wiring up the wheelarch etc went to connected it in under the bonnet but the connectors on the end of the sensor wire won't mate with the sensor on the car - it doesn't have the gap to accommodate the triangular shaped thing. The connector is also white not black - dont know if this indicates its off another model. This left me in a bit of pickle

* I didnt want to hack the wiring loom of the car to accommodate a sensor that might be wrong
* I didnt want to hack the wiring from the sensor, because if it's wrong I wanted to send it back
* I was now worried the sensor wouldn't work at all.

Given the above I decided the best course of action would be to just jury-rig the connectors together using two pieces of wire and insulating tape. I did reason if the it didnt work would it could have been because this arrangement was adding resistance/losing voltage or causing/allowing interference so a failed test wouldn't tell me anything.

In the end I need not have worried. I flick the ignition on and the ABS came on and went out... RESULT !!! I was under the impression i'd have to drive the car to let the ABS ECU know it was all working again but I didn't. The light being out is all I needed for the MOT and all my previous jags haven't had ABS anyway so I wasn't that bothered about the system actually being operational, I could deal with that later.

But curiosity got the better of me and I took her down to a large office car park out of hours. I backed up to one end accelerated to about 30mph and then just mashed the brake pedal. She chripped a tiny bit but pulled up straight and true with no noticeable skid. I had tried exactly same test a few weeks previous when the light was still on and she skidded about 5 meters. I tried a good number of times more and couldn't get her to skid - even on looser surfaces. So I don't just have a light out, I actually have an ABS system.

I need to find a more permanent solution to the connector problem, which involves either swapping the end off one of my three broken sensor, or sending this one back and getting the right sensor - which seems easier said that done. But I now know that if the sensor that's in the car can be connected then I have ABS.

I'm pretty much going to consider the thread closed at that, although I may post an update about what I did re the connector.

So thanks so much to everyone for all their help, particular LeeP - I'm not sure I'd of got this far without someone pointing out the obvious when I was making dumb mistakes.

Now it's onto the power steering.... I'll start a new thread.


Simon


As an aside, I'm actually super impressed with the amount of extra braking the ABS system gives you. I was always from the school of thought that an ABS doesnt give a good driver much less stopping distance. I've never had a significant lockup on my other jags so I figured I was fairly decent at braking. Having felt the amount of force the ABS can muster without skidding has shown me I wasn't using the brakes to anywhere near their full potential. The initial stages were similar to what I would have managed but the last few foot where the weight is already all the way over the front wheels, the ABS system really lets them bite down, where as I would have left it with much the same force as the initial phase for fear of locking up. I think I've had an eye opener for when driving an non ABS model

 

Simon,

Great to hear that it sounds like you've finally got there! Well done for persevering!

Paul

 

Well done Simon - great to hear a Jag story with a happy ending!
Cheers,
Lee