75ZT Community

Hello, Ihave a mg zt-t 2.5L V6 190 Ps with a new intersting problem.(car with abs and traction control)
When i press the brake pedal and the car reach the 40 km/h a crispy noise and a "clong" comes assiocated with a bad feeling on the pedal.
the symptom diseapear when the speed decrease.(pressure applied to the pedal brake didn't change anything).
No fault on dashboard, and all bushing (steering and suspension) of the car have no exessive play
Have you an idea of witch component is probably faulty.
thanks for the reply.
Vincent

Often there can be a problem with the wheel speed sensor or the magnets that the sensor sees. The most common seems to be flakes of rust coming from the backplate on the rear wheels and this gets into the gap between the sensor and the magnets. Sometimes the magnet ring gets damaged, but this is most often when a sensor gets replaced. Also some replacement sensors are not genuine and are not always reliable.

Thanks Duncan,
Yes today i try to remove the fuse of the ABS (Antilock Braking System) in the dashboard, the result is no problem with the brake pedal and no crispy noise when you apply the brake at around 40 Km/h. The car go the next week to the mg dealer for test book apliance to see if any fault is recorded insiside memory. But probably you are right with your diagnose. Probably an abs sensor send wrong info to the abs modulator.
I put more info if i have the next week.
thanks for reply
Vincent

Hello folks
More trouble shooting on going:
Mg rover dealer apply test book no fault stored,clean all abs sensor,the problem is still present.
Mg rover did n't help more.
I suspect one solenoid inside the abs module is faulty (not permantly) next step is to replace the abs module with reprograming and the 4 abs sensor.
More info when i receive the parts from UK and module is reprogramed.
Vincent

I would suggest the "no fault stored" outcome points to a failing wheel bearing. If the ABS module was at fault it would show a fault code. I believe that the T4 (Testbook version 4.Computer Diagnostic System) live data would show you which wheel is reporting as no rotation but Duncan will confirm. If you have no access to live data then you will need a multimeter to diagnose each wheel sensor/bearing.

takestock wrote:I would suggest the "no fault stored" outcome points to a failing wheel bearing. If the ABS module was at fault it would show a fault code. I believe that the T4 live data would show you which wheel is reporting as no rotation but Duncan will confirm. If you have no access to live data then you will need a multimeter to diagnose each wheel sensor/bearing.

Hi Dave
T4 should show which bearing is at fault, it did on my MGZT back in 2016

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Agreed, on total failure of the magnetic bearing the sensor would report back no movement then the T4 would register as you have shown. What about a bearing that only has a few segments failed it could/would report back as a slower rotation and invoke ABS when not required? If this was the case then the T4 would not think anything was amiss?? What do you think

Hi Dave.
If that was the case and you do not have access to aT4 then you may well need one of these below.
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Mark of the tyre segments as the using multimeter to diagnose each wheel sensor.
One should read 0.67
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Next segment 1.72 and so on i think 46/47 in total any gaps and you have found the problem.
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you can earth on the door.
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this is at the rear which most of the time it's the OS bearing.
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T4 will also show this sometimes.
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Recently had this on Ed and ended up having the the O/S/R bearing replaced three times, (thankfully at the garages cost) and ended up having to fit a genuine sensor (from DMGRS) before the problem was finally sorted! Just make sure who is replacing the wheel bearing, uses a genuine bearing and a genuine sensor, otherwise you're in for a whole world of pain with it!

Hello,
If i have been understood the recent post, one eventual failure of the problem maybe comes from wheel bearing.

And for artic "the value show on the multi ( value of 1.67 ohm) is between each notch of the abs rim and you need to control the value of the sensor for each notch (aprox 46 47 notch for one 1 rim per wheel)
I have been understood correctly or not?

For info i am not car mechanical and my speaking languages is the french.
Thanks for all for the interesting replies about this problem.
Vincent from Switzerland

Your understanding is correct. The most common failure is rear bearing on the right.

One more question wich system is installed on the ZT-T for the ABS a passive system sensor type 1 above(picture from hella) or a active system sensor type 2 below on the picture

Below is an explanation courtesy of( HarryM1BYT ) on the OC


The sensors are entirely solid state electronic Hall Effect devices. Contrary to some websites which suggest they have a coil of wire inside the Hall sensors - they absolutely do not, they are entirely solid state.

There are two types of Hall Effect device, an HE Sensor and an HE Switch. Our er - 'sensors' use HE Switches.

1. An Hall Effect Sensor produces a variable output, depending upon the strength of the magnetic field.

2. An Hall Effect Switch, closes at above a certain level of magnetic field and opens below that level. The switching point is very sharp.

An Hall effect device produces an output whether the magnet is moving or stationary, which means it can work from zero mph. The older style coil sensor can only sense a magnet when the magnet moves, no movement no output. Using coils would not allow our speedo to work so well at extremely low speeds.

A further difference which becomes important when trying to test the ABS sensors is that the coil type can be tested for resistance with just a multi-meter. If you know what the resistance should be, you can get a good idea as to whether they are good or bad simply by measuring the resistance. As said, this once worked fine on the older coil type sensors, but not now, but many brought up on the coil type of ABS sensor still do suggest you can simply check the resistance.

It is entirely pointless try to do the same with an Hall Effect device. You simply cannot check them by measuring their resistance, they have to be checked in some sort of active circuit and in a two wire version like ours, by measuring the voltage and watching for the sharp switching points as a magnetic field passes by them.




I would plump for the OS rear bearing myself, rust from the back plate can effect the magnet ring.
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many thanks for the explanation
Vince

That explanation of our sensors, is the best I have seen and is spot on.

Hello 75zt community, I have received the parts and i will try first the replacement of rear bearing.
Many thanks
Vince

Thanks for keeping us informed

Many thanks for all the 75 zt community, after replacement of rear bearing all problem with the ABS trouble was fixed.
I verry apreciate your support with this particular and interesting trouble, the MG Rover official dealer didn't now the trick.
Problem solve.
Merci Vince

takestock wrote:Your understanding is correct. The most common failure is rear bearing on the right.

Can I claim the points on this one then

I have one to sort out tomorrow along with cleaning the back plates and drums