Hi All,

Me again...

Sorry to start a new thread on my quest to remedy a P1642 code, but I thought the "XJR with Relentless P1642 Fault Code!" thread had become somewhat fragmented. (https://www.jaguarforums.com/forum/xj-x308-xj8-xjr-27/xjr-relentless-p1642-fault-code-86431/)

While I await delivery of an Autoenginuity OBD device & Jag Enhancement software I thought I'd carry out some further checks.

One was to test the continuity of the CAN-Bus which confirmed 120 Ohms and believe this is spot on.

Another was to check the wheel speed transducers by measuring their resistances. Firstly at the ABS module socket where all sensors returned a reading of between 1.081 and 1.089k Ohm's. Then again at each sensor after removal and thorough cleaning where the results varied between 1.088 and 1.091k Ohm's.

Clearly the tolerance range between all the sensors is negligible and was quite pleased with this overall. But, I have found conflicting information on this site as to what the resistance readings should be. (One post mentions 2.014k Ohms, and another 1.06 Ohms). Could someone please clarify what the manufacturers design tolerance / range is please as mine are poles apart from these.

I also noted that the resistance increased and dropped significantly when a ferrous metal object was passed close to the face of a sensor (typically 0.821 - 3.141k Ohms). Therefore, presumably there could be a significant difference in the accepted resistance depending on whether the sensor is fitted in the calliper pocket or not?

One final question, the speed sensor 'toothed rings' fitted to the rear of the stub axle appear very corroded in the front IMO. I understand these are screwed on and secured with a spring clip, but require a special tool to remove/replace available for the gifted price of £150. If these were to be renewed would anyone condone their replacement using a hammer & chisel?

Thank you in anticipation.
Chris

 

I and several others have observed resistance readings similar to yours. I don't think the actual number is critical. As to removal of the ring, again several posts have suggested using hammer and chisel, then fitting new rings as the most cost effective method.

 

I cannot recall the size, but I got a Chinese 12 pt. socket at the local junk tool store that fit the ring well enough to get it off.

As to the difference in reading "when a ferrous metal object was passed close to the face of a sensor"; I think you will find the key is when the ferrous metal is actually moving it is inducing an emf that you see as a resistance change. When still, there should be no change.

 

Hi,

RJ - Thank you for giving me some comfort here. It would be good to know what the manufacturers accepted resistance range should be if anyone happens to know, or if anyone has measured this on a new sensor.

Ross - Them Chinese are cleaver dudes! Any chance of popping over for a loan of your socket?

Before I attempt to remove the 'speed sensor rings' can anyone confirm if they are normal thread (clockwise to tighten) or opposite thread (anti-clockwise to tighten), and if they can be removed with the front stub axle in place? Something I'd like to get right before attacking them with a hammer & chisel!

Thank you.

 

I used a 2" 12 socket to remove the front wheel speed sensor ring. Grind down the face of the socket to remove the tapers on the 12 points so the socket will grip the ring better. I used a impack gun mainly because I could not secure the keep the hub assembly from spinning on the floor while trying to use a breaker bar.

Is your ABS light lit?

 

Hi Rocklandjag,

Unfortunately, I don't have a socket that big (yet). After a good soaking in WD40 overnight I tried to remove the speed sensor rings using a cold chisel & hammer (with hub still attached to car). All I managed to do was break a number of 'pimples' off the back of the ring. I even tried some heat treatment using a blow torch but they wouldn't budge!

Looking at the fine thread on the new rings I suspect the old ones are well and truly corroded in place after 13 years. Also the spring retaining clips had pretty much turned into dust.

What initially looked like a straight forward replacement has developed into another interesting problem.

I'm now considering cutting two slots in the rings at 180 degrees and trying to split them open. However, my main concern now is what's actually what's left of the hub assembly thread when/if I ever remove the old rings?

BTW, ABS light is intermittent but regular together with 'No Trac' / No ASC / R.P. And sometimes Failsafe Engine Mode if I'm really lucky!

 

Why is it you are determined to remove the rings? I had to do it to replace the bearings, but the hub was off the car.

 

If you have the ABS light along with the others on an intermittent basis my guess is you have a bad connector or wire connecting the speed sensor to the main wiring harness. i would start with the front wheels. Disconnect the wire where it connects back to the frame. Put an Ohm meter on the wire and then wiggle the wire and wiggle the connector at the speed sensor. The cable from the wheel sensor to the body was the problem on my car.

With an intermittent problem it is very unlikely to be the speed sensor ring. Hopefully you did not fry the grease in the wheel bearing using a torch. Also, even if you get the old one off with the chisel you will still need a socket to tighten and torque the new one

 

Hi Ross,

Determination is not quite the issue. Having tried pretty much all the fixes and advice I've found on this forum (and others to be truthful), and as part of my ongoing quest to remedy the random, but very regular ABS Light / No Trac / No ASC / RP fault I thought I'd try some other potential fixes while I await delivery of my Autoenginuity scan tool which will hopefully read any ABS 'C' codes etc.

Having removed cleaned and checked the speed transducers, connecting leads, connectors and fixed wiring harness my attention was drawn to the heavily corroded wheel speed sensor rings. Initially these appeared to be a simple low cost task to renew, but clearly I was mistaken! Sure, they're low cost but the old ones are a bugger to remove.

I acknowledge that if the rings were corroded to a point where the hall effect could not be properly transmitted to the ABS module then the fault would probably not be intermittent but permanent. However, there must be a point where they reach the outer threshold of the manufacturers specification. I assume this can be determined by the clearance gap between the sensor head and ring? However, I haven't come across the accepted gap tolerance as yet.

I also note that the theory of measuring the resistance of the sensors 'may' be a red herring. Referring to the Jaguar XJ308 Workshop Manual (Extracts attached here -https://dl.dropbox.com/u/69683559/Pa...p_Manual-2.pdf) the method of testing them is to measure their voltage output while spinning the wheels. Apparently, they should produce from 0 - 5vAC (measured using a multimeter set at Volts AC), and concur that having carried out this test a voltage of between 0 & 2.7vAC was measured by spinning the wheels by hand only. The Workshop Manual makes no mention of testing the sensors resistance. I'm not sure if this clears up the earlier confusion over the range of different resistances I've seen reported, or just clouds the issue further, but hey ho...

 

Gotcha-
I doubt it is the rings, but you never know. Have you tested the resistance for each sensor at the ABS module? And I am almost certain the sensors are variable reluctance coils, not hall effect. There is a magnet and coil at each one and the passing teeth induce a pulse into the coil.