ABS Testing

I finally got around to testing the ABS signals on my ZTT, although this method of testing would work exactly the same way on a F or TF.
May be worth adding this post to the How to sections if you think its worthwhile.

The fault is a slight pulsating on the brake pedal when braking. I suspected a possible issue with the ABS monitoring which would cause such a problem, so this needs to be checked and proved out!

I will explain how to test with a Digital Multimeter and an Oscilloscope.
First with the multimeter...you will need a meter that measures dc volts, such as this one.



Jack up the car and remove the wheel that is to be tested, on this set of pictures its the rear wheel of my ZTT.
Find the plug for the ABS sensor for this wheel - on the ZT its a blue connector, on the F and TF its a creamy white colour and the rears sit in the engine bay and the fronts under the bonnet. You then need to connect on to the signal wire of the sensor. One wire is a 12V feed to the sensor, the other is the signal back to the ABS. I scraped a bit of insulation off and tested each wire until I found the one which is not the 12V feed but the signal wire. Connect on to this with the red wire of the multimeter and connect the black wire to a good earth point.
Don't forget when you have finished the test to tape up the insulation again!



Then if you spin the wheel hub you should see the voltage reading on the multimeter jump from about 0.7v to 1.7 volts. (sorry I do not have a picture to show this as I used my oscilloscope in the actual test). Place a mark on a reference point or you could use the edge of the brake caliper so you know where to mark the brake disc during testing. I used a white paint marker to mark the reference point.
Then rotate the wheel until the multimeter jumps from 0.7 to 1.7 volts and place a mark on the brake disc. Rotate again until the meter drops back to 0.7 volts and goes back up to 1.7 volts again and make another mark. Repeat this process marking each high point.
In the picture below I made a mark on the top of the brake disc rear guard as a reference and you can see the marks where the signal goes high painted on the disk.



Continue until you have completed one revolution. you should have something like this.....

.

If you have any gaps where there should be a white mark, you know you have a pulse missing from the ABS reluctor ring. Go back and double check. This would suggest that the ring is damaged or there may be a build up of corrosion in the sectors of the ring. If you get no pulses at all, you may have a faulty sensor. If a sensor is faulty, then the ABS light should have come on anyway.

Now how to test using my oscilloscope, this is a cheap £20 unit I bought off ebay. I made a simple power supply to run it from my 12v outlet on the car.
This power supply is shown in the metal box to the left in the picture.



Again connect the red wire of the oscilloscope to the signal wire of the sensor and and the black wire to a good ground point.



Set the oscilloscope to read 1 volts per division and and use a nice slow timebase of say 10 milliseconds. Spin the wheel and you should get a nice trace of square pulses on the oscilloscope screen such as this...



If there is a gap in the regular sequence of pulses, then you know you have a segment down on the reluctor ring.
I did try to load a video up of the scope in action, but the forum will not load the Imgur file. I may see if it will load on another post direct from my PC.

The good news is all of my sensors are looking ok and test out fine with no pulses missing. So I will now look at the rear discs since the front ones are new. The discs are about due to be changed anyway!

Sundance

SundanceUK wrote: I finally got around to testing the ABS signals on my ZTT, although this method of testing would work exactly the same way on a F or TF.
May be worth adding this post to the How to sections if you think its worthwhile.

The fault is a slight pulsating on the brake pedal when braking. I suspected a possible issue with the ABS monitoring which would cause such a problem, so this needs to be checked and proved out!

I will explain how to test with a Digital Multimeter and an Oscilloscope.
First with the multimeter...you will need a meter that measures dc volts, such as this one.

Jack up the car and remove the wheel that is to be tested, on this set of pictures its the rear wheel of my ZTT.
Find the plug for the ABS sensor for this wheel - on the ZT its a blue connector, on the F and TF its a creamy white colour and the rears sit in the engine bay and the fronts under the bonnet. You then need to connect on to the signal wire of the sensor. One wire is a 12V feed to the sensor, the other is the signal back to the ABS. I scraped a bit of insulation off and tested each wire until I found the one which is not the 12V feed but the signal wire. Connect on to this with the red wire of the multimeter and connect the black wire to a good earth point.
Don't forget when you have finished the test to tape up the insulation again!

Then if you spin the wheel hub you should see the voltage reading on the multimeter jump from about 0.7v to 1.7 volts. (sorry I do not have a picture to show this as I used my oscilloscope in the actual test). Place a mark on a reference point or you could use the edge of the brake caliper so you know where to mark the brake disc during testing. I used a white paint marker to mark the reference point.
Then rotate the wheel until the multimeter jumps from 0.7 to 1.7 volts and place a mark on the brake disc. Rotate again until the meter drops back to 0.7 volts and goes back up to 1.7 volts again and make another mark. Repeat this process marking each high point.
In the picture below I made a mark on the top of the brake disc rear guard as a reference and you can see the marks where the signal goes high painted on the disk.

Continue until you have completed one revolution. you should have something like this.....

.

If you have any gaps where there should be a white mark, you know you have a pulse missing from the ABS reluctor ring. Go back and double check. This would suggest that the ring is damaged or there may be a build up of corrosion in the sectors of the ring. If you get no pulses at all, you may have a faulty sensor. If a sensor is faulty, then the ABS light should have come on anyway.

Now how to test using my oscilloscope, this is a cheap £20 unit I bought off ebay. I made a simple power supply to run it from my 12v outlet on the car.
This power supply is shown in the metal box to the left in the picture.

Again connect the red wire of the oscilloscope to the signal wire of the sensor and and the black wire to a good ground point.

Set the oscilloscope to read 1 volts per division and and use a nice slow timebase of say 10 milliseconds. Spin the wheel and you should get a nice trace of square pulses on the oscilloscope screen such as this...

If there is a gap in the regular sequence of pulses, then you know you have a segment down on the reluctor ring.
I did try to load a video up of the scope in action, but the forum will not load the Imgur file. I may see if it will load on another post direct from my PC.

The good news is all of my sensors are looking ok and test out fine with no pulses missing. So I will now look at the rear discs since the front ones are new. The discs are about due to be changed anyway!

Sundance

Great how to. It’s probably the off side wheel bearing. There’s a magnetic ring in the bearing


Sent from my iPhone using Tapatalk

NigelOBB wrote:
Great how to. It’s probably the off side wheel bearing. There’s a magnetic ring in the bearing

Are you sure?

ABS is usaly from a reluctor ring (a bit like a toothed gear) fastened on the outer driveshaft joint!

G0RSQ wrote:

NigelOBB wrote:
Great how to. It’s probably the off side wheel bearing. There’s a magnetic ring in the bearing

Are you sure?

ABS is usaly from a reluctor ring (a bit like a toothed gear) fastened on the outer driveshaft joint!

Was the bearing on one of my 75s. There’s a few bits about it on the oc.


Sent from my iPhone using Tapatalk

Yes the rears have the reluctor ring around the end of the bearing face, the sensor is in line with the drive shafts pointing in towards the bearing edge. Anyhow, all four reluctor rings test out perfect with all of them not missing any pulses. The front have a more conventional ring with serrations in. I am looking at the rear discs now, which I am hoping will cure the fault. I have fitted new discs on the front a couple of weeks ago ready for the upcoming MOT.
The little hand held scope is a fantastic bit of kit for the money and worth having for the 20 quid it cost me.

Sundance

SundanceUK wrote: Yes the rears have the reluctor ring around the end of the bearing face, the sensor is in line with the drive shafts pointing in towards the bearing edge. Anyhow, all four reluctor rings test out perfect with all of them not missing any pulses. The front have a more conventional ring with serrations in. I am looking at the rear discs now, which I am hoping will cure the fault. I have fitted new discs on the front a couple of weeks ago ready for the upcoming MOT.
The little hand held scope is a fantastic bit of kit for the money and worth having for the 20 quid it cost me.

Sundance

I went through the same process as you it to a while to get an answer. Mine went through a couple of mots before I changed the hub assembly ( it’s easier than replacing the bearing ) and stopped the prob, the bearing has a magnetic ring built into the seal. It could also be a mucky sensor. There’s plenty of info on the 75 and ZT OC.


Sent from my iPhone using Tapatalk

SundanceUK wrote: Yes the rears have the reluctor ring around the end of the bearing face, the sensor is in line with the drive shafts pointing in towards the bearing edge.

Sorry, missed the bit in the first post that you were looking at a ZTT. Assumed it was an F or TF :oops:

SundanceUK wrote: Yes the rears have the reluctor ring around the end of the bearing face, the sensor is in line with the drive shafts pointing in towards the bearing edge. Anyhow, all four reluctor rings test out perfect with all of them not missing any pulses. The front have a more conventional ring with serrations in. I am looking at the rear discs now, which I am hoping will cure the fault. I have fitted new discs on the front a couple of weeks ago ready for the upcoming MOT.
The little hand held scope is a fantastic bit of kit for the money and worth having for the 20 quid it cost me.

Sundance

How are you getting on with the diagnoses


Sent from my iPhone using Tapatalk

The sig gens work well, and they have the same plug fitting as the scope, so the same PSU can be used. Its not very clear which way the electrolytic capacitors are fitted on the board, I think if I remember correctly the -ve leg goes to the shaded part on the circuit board mimic. Use a google search photo just to make sure. Also when soldering the potentiometers, they have to be seated as close to the PCB as possible or the knob will foul on the box lid.

I will be checking the wheel bearings when I do the discs. I have ordered some new stake nuts for them.

Sundance

Loving the electronics. I miss having a function generator and scope at work. These would be perfect at home, especially audio work. I'll get them.