If you have any questions prior to purchasing the kit post them here.
Following on from a recent forum post re ABS diagnosis and AC Coupling post85541.html?hilit=ABS#p85541
It occurred to me that there is an element of doubt that creeps into ABS sensor diagnosis where Magnetic Pole Pick-Up Rings are utilised to generate a wheel speed signal.
In a scenario where the Wheel Speed Sensor is functioning but the Pick Up ring magnetic field is broken or reduced in “field” strength, a speed signal output of some form would be evident.
However, the signal may be sporadic, deformed or sequentially non-uniform if damaged in a single location about its circumference. Hopefully accompanied with an implausible signal code via the ABS controller.
What about a scenario where the wheel speed sensor is not functioning and we wish to qualify the pick up ring?
Whilst diagnosing MRE Wheel Speed sensors can be carried out conclusively with PicoScope the same cannot be said for Magnetic Pole Pick-Up Rings integrated into the Wheel Bearing or Hub Assembly
With the wheel bearing removed this is simple with a “Field Finder”:
In the real world, to get to the stage in the image above can incur an enormous amount of work and so diagnosis of the Pick Up ring is a leap of faith.
There is another way using the Pico TA330 Keyless Entry Detector, which by its operational characteristics becomes “excited” about a magnetic field!
With the Wheel Speed Sensor removed and the Keyless Entry Detector inserted into the Hub assembly we can determine the integrity and orientation of the Pick-Up Ring
With the Wheel Speed Sensor removed, insert the Keyless Entry Detector into the sensor aperture so as to bring the sensor tip into close proximity to the Pick Up ring.
Using the scaling and filtering feature of PicoScope, select a 50 mV input range, increase the scaling by a factor of 10, and activate the default Low Pass filter of 1 kHz. Now rotate the wheel assembly paying attention to hands and fingers in relation to the brake caliper and suspension components!
The Keyless Entry Detector will generate a sufficient sine wave in order to serve as an indication of the Pick Up ring condition and orientation where a new wheel bearing may have been installed.
The waveform below demonstrates this exact technique
Whilst this will prove an invaluable step during diagnosis a number of modifications will be required to the TA330 Keyless Entry Detector
The photo above (Keyless Entry Detector) demonstrates the use of the first generation TA330 with the reinforced cable insulation extended over the sensing tip of the Keyless Entry Detector.
Whilst the insulation provides stability to enable insertion of the sensor into the Hub, the insulation had to be cut about the sensor tip as the diameter exceeds the size of the sensor aperture within the Hub assembly
Looking at the existing TA330 this would require a rework to the surrounding insulation which is far more robust.
Rest assure we are looking into this as a future modification to the existing design.
Moving on slightly, not only is the Keyless Entry Detector tuned to detect the carrier frequency of keyless entry systems (125 to 140 kHz) we can be see above it is also an inductive pick up which opens up other measurement possibilities.
If that wasn’t enough, the Keyless Entry Detector is a Capacitive pick up too.
More to follow soon
I hope this helps, take care…….Steve
As Steve mentioned the tool is excited when it sees a magnetic field and we all know that an engine bay has rather a lot of this floating about. Better still some of this can be picked up with the keyless entry detector. A lot of the work I’ve done so far has only been with Common Rail Diesel engines but I’m sure more ‘uses’ will be added as we continue with the journey.
Have we ever been in a situation where the injectors are stuck under an inlet manifold or tucked under a bulk head and to get to back probe the connector will result in the tops of knuckles being scrapped off? This is something that crossed my mind and there are times when just a quick check will be more than sufficient to confirm an event has taken place. Enter the KED! With the below capture I’ve back pined injector Number 1 and added a current clamp just to be sure that the signal I was getting from the KED was what I thought it was and it matches perfectly!
As you can see, the inductive kick we see when an injector is turned off excites the KED and then displays this for us to show activity but we can also see activity when the it is turned on and during the holding phase. In some situations this may be all we need to help with our diagnosis if we suspect an issue with an injector.
This made me think further about what was happening and if we can see activity at the injector where else can this signal be seen. My thoughts turned to VW’s PD engine where the injectors are under the cover and the wiring can be tricky to get to. Just to be clear the capture below wasn't from a PD engine but the technique could still apply. I've kept the reference to cylinder 1 injector to confirm signal and offering up the KED to loom had surprising results.
Just by holding the KED at the loom all 4 injector events, or activity, can be seen. For a quick check to see if there is activity without having to dig the injectors out, the KED will hopefully make life a little easier. Of course the amplitude of the signal will greatly depend on where and how close the wiring is to the KED but it can still be seen.
As I mentioned before, this method has only been used on a Diesel at present and as further testing takes place we will update this post.
I hope this helps
You are most certainly correct that you don’t need a KED to confirm the integrity of the Pick Up ring when you have a functioning ABS sensor.
My thoughts are aimed at qualifying the Pick Up ring whilst you are diagnosing a faulty sensor.
This way we can inform our customer both a wheel bearing (with pick up) and sensor are required in a single diagnosis.
The other scenario is qualifying the Pick-Up ring where a new sensor has been installed but the fault remains.
I hope this helps, take care…….Steve