Has anyone run into this situation?

I have a persistent Anti-Lock failure lamp illuminated on the dash. It started about a month ago as an intermittent failure. Potholes and large bumps would trigger the lamp, and typically, the lamp would be off when starting the car. I was unable to get any codes with the Blink Test because the lamp would be off until the car was driven. When turning the ignition off then on with the diagnostic connector shorted, no codes would be displayed. So I waited.

Now the code is on all time time, as soon as the ignition is turned on. I figured this would make it easier to get a readout of the failure code in memory. Not so. I still am not getting any flashes from the indicator. When the diagnostic connector is shorted (black & brown/pink wires), and the ignition turned on, the Anti-Lock lamp remains OFF. If the car is started with the connected shorted, the lamp comes on. But again, when cycling the ignition, the lamp remains off, even after the supposed 6-second delay before codes should be displayed. Nothing, no flashes at all.

Both ABS pump and main feed 30A inline fuses above the inertia switch are present and intact. I have cleaned and re-seated the main ABS ECU connector. Could this be an ECU failure? Intermittent failure of the power feed wires or relays?

-Nick

 

Hi Nick,

My first suspect would be a wheel speed sensor or its wiring harness. A method for testing the sensors and their wiring at the same time is to disconnect the main connector at the ABS module and test the resistance across each sensor's terminals, then flex the wiring harness along its length between the sensor and body while watching the meter to see if the resistance changes. If the resistance changes when you flex the harness at a certain point, you've found a break. If the resistance of one sensor is open (infinite resistance) or shorted (0 ohms or close), or if the resistance is significantly different from that of the other sensors, suspect sensor failure. Off the top of my head, most ABS sensors I've measured have been in the 1,500 to 2,500 ohm range (1.5 - 2.5 Kohms).

Another possible issue is that the magnetic field of the sensor has attracted metallic brake dust that is interfering with the sensor's operation. Cleaning the sensors and reluctor wheels may cure the problem.

Water ingress into the ABS module is a known issue when the rubber gaiter around the fuel filler neck develops leaks.

I don't remember this being a problem on XJ40s, but on the X300s and X308s a very common issue is cold/starved/cracked solder joints on the circuit board in the ABS module.

 

Thanks Don. I suppose that check resistance check could be just as useful as the fault codes themselves. Years ago I did have a light on due to a LR sensor harness issue, which I corrected. Maybe it needs to be repaired again?

It makes sense that the light would be setting right when the ignition is turned on if the ABS ECU seeing an open/short in one of the sensors. I suppose a dirty or failing sensor would more than likely set off the light only after the vehicle is driven above the self-test speed? A clear open/short would be much easier to track down with a multi meter at the ABS connector than a sensor that's on its way out, lets say.

I'm just really puzzled as to why the diagnostics isn't working. I have successfully read codes before that way.

Nick

 

What is the condition of the rubber gaiter around your fuel filler neck, and is the drain clear?

Is it possible that you can't read the diagnostic codes due to a problem with the ABS module itself, such as water ingress or corrosion on the connector? It might be worth disconnecting and cleaning the connector at the module and whatever ground point is referenced by the module (probably one of the ones in the trunk).

 

Gator is intact and the drain is clear. That side of the trunk has always been bone dry. My problem area with water was the RH side of the trunk in the ventilator box area.

I guess it wouldn't be a bad idea to clean the pins of that diagnostic connector after disconnecting the battery, and give it a little DeoxIt. I've already cleaned and reseated the large, main ABS connector. Seeing as the Teves ECUs are pretty easy to come by online for under $50, I could always pick up another and keep it as a spare if it turns out to make no difference.

Admittedly, I have on a couple of occasions, shorted the wrong wires when attempting to read the codes. Both times the 30A ABS ECU inline fuse above the inertia switch blew. Maybe that affected the diagnostic circuitry of the ECU?

Thanks a bunch, Don. I've got a few solid leads to follow here. I will report back with my findings after I probe around a bit with the multimeter.

Nick

 

Spent some quality time today with the ABS wiring diagram and Jaguar’s test procedures.

When checking the Right Rear wheel speed sensor for resistance, I got an open.

Jacked the car up, removed the wheel and to no one’s surprise, the insulation on the sensor lead is very brittle and cracked/missing in multiple spots.





I had the same issue a few years back with the LR sensor, but the issue was confined to one area so I repaired it. This one seems a bit too far gone.

Does anyone know if a LF or LR sensor would work in the rear? (Is the lead long enough?) I’m seeing $230 as about the cheapest I can get a new OE sensor. Not much luck finding used. Standard Intermotor sells an aftermarket, which appears to have the benefit of more modern insulation on the lead while retaining the original grommets and convoluted tubing at the correct points, but it’s even more expensive than the original from Jaguar.

I’ve soaked the sensor body in penetrating oil and have given it some wiggles to let it seep down around the hub in preparation for replacement.

Maybe I should just repair this one too?

Nick

 

Hi Nick,

I don't know if the lead of a front sensor will be long enough. A LR sensor may work if the indexing of the mounting tab doesn't present a problem. But as long as your sensor isn't damaged, I don't know why you couldn't just replace the entire section of deteriorated wire with a section of shielded microphone cable carefully soldered in and sealed with heat shrink tubing.

Maybe others will have an even better idea.

Cheers,

Don

 

You know what, Don? I think I may go that route... I've always deferred to your good judgement, and it's never let me down. Plus, my soldering supplies are all stocked up, and I just got a new tip in for my Ungar station. This would be a good first job for it.

That sensor price is hard to swallow... And I'd rather not run into issues removing the sensor from the hub if I can avoid it.There's good working access with the flying lead removed from the trunk.

I'm planning on doing an oil change and lubrication today, so I'll take a closer look while the rear is in the air for the greasing, and see where I end up. if I can shrinkwrap the more minor areas on the insulation, repair the break and shrinkwrap that, I think I can get away with a wrap of high quality electrical tape and convoluted tubing the entire length. Why did they have to go with flying leads for everything on these cars!?

Nick

 

So it would be easy to repair the leads by soldering?

Larry

 

Lots of the other makes have similar wheel speed sensor leads - BMW, Mercedes, etc., so it's not exclusively a Jaguar issue. I recently repaired the lead on a rear E46 BMW wheel speed sensor that had been chewed right through by a rodent.

 

Spent some time yesterday rebuilding the ABS sensor.

I had previously sprayed the sensor down with penetrating oil and thankfully I was able to get it out gingerly with alternating prying motions under the sensor itself, while also turning it left and right. I definitely was sweating until it emerged in one piece.

The cable is a single conductor with a braided shielding. My shielding was corroded all over and split in many places due to cracked insulation.

I didn’t have much on hand, but I had the wild idea of replacing the lead altogether with coaxial cable. Single conductor with braided shielding. Outdoor rated insulation, somewhat flexible. I assume it’ll last at least a year or two now that it’s soldered, shrinkwrapped, taped with quality electrical tape, and covered with convoluted tubing. I know it’s not exactly the correct solution, and vehicles should always use stranded wiring, but it’s what I had on hand, and I didn’t want to build an unshielded wire and risk a flaky signal mid stop during an ABS application.




Resistance of the assembly is 1.12k ohm which is right within spec of 0.8-1.4k ohm.




So far so good, the light was extinguished as soon as I turned the ignition on, and stayed off after the drive-off self test.

Nick

 

Good job, Nick! You may find that your repair outlasts the car!

Cheers,

Don