ABS diagnostics aid - free loaner

[HarryM1BYT]

Reece (RROBSON) dropped in earlier with some long promised ABS plugs and sockets. Thanks Reece!

Idea is to make what used to be called a 'break-out unit or box'. A back to back plug and socket, giving you easy access to test the ABS sensors for signal, when plugged in line between the existing ABS plug and socket.

The choice is yours, as to whether you use a meter, a piezo or both. Using a meter on the 20v range across the wires, watching the fluctuations of voltage as the wheel is very slowly rotated with ignition on. During my own test with the unit, as the wheel was rotated, it registered a step change from 9.39 to 10.40 then back to 9.39v across the two terminals of the ABS, the actual value depends upon the state of charge of the battery, but what is important is the 1.0v difference between the two, as the wheel is slowly rotated and its regularity.

I've written a bit of an explanation of how the sensors work here, to help dispel some of the myths - http://www.the75andztclub.co.uk/foru...37#post1765137

Basically jack the wheel off the ground, plug the unit in, connect your 20v meter one probe to each wire terminal of the unit or listen to the piezo. Then put a brick or similar heavy item on the ground next to the wheel and whilst very slowly rotating the wheel, mark with chalk on the tyre where the meters reading changes low to high or at every second click of the piezo, using the edge of the brick as a reference point for marking. If all is OK, you should end up with a series of marks, all perfectly evenly spaced around the entire perimeter of the tyre. If there is irregular spacing between the chalk marks, or no signal detected you have found your problem sensor.

What I would suggest whilst you have these plugs and sockets apart, is to put a smear of Vaseline or WD40 around the seal. Its not that they leak, rather that they can be so tight and in such awkward locations it can be very difficult to part them due to the tight seal and both stiction and suction.

Instead of the above unit, you could almost as easily tap into the two wires, using the old method of pushing sharp needles through the insulation - this just makes it that bit easier and more certain of making a connection.

As usual with such free to loan items, I will need my costs to be covered, via Paypal payments, sent as two separate 'friends and family' payments.

The first £7 (cost increased to help recover my costs) to cover P+P, the second a deposit of £10 simply to ensure I get them back. As always, you get the full £10 returned just as soon as they are delivered safely back to me and undamaged. Please get a receipt for posting just in case, then you can claim from Royal Mail if it does go missing. For those who local, you are welcome to just collect and return for £10 cash deposit.

You make a request for the loan by email please click HERE, put in the subject line 'ABS DIAGNOSTIC' - that avoids it being trapped by my spam filters.

I will soon have several of these basic units available for loan, then I will see if I can improve on the idea.

[UPDATE] I've been giving this some thought, trying to find a simple way to indicate the the passing of a segment, without getting involved with complex electronics, comparators and LED's. What was needed was something easy, which would detect the sudden swing from 9.?v to 10.?v as each segment passed the sensor, preferably something you could hear and which did not disturb the normal function of the ABS.

The solution is a piezo sounder (or speaker) or a piezo earpiece, not the sounder with a built in oscillator to produce a tone when 5 or 12v is applied, but just the bare item - a thin disc with two wires attached or a piezo earphone.

Once connected in line, you hear a slight buzz, then as a segment passes the sensor and the voltage changes, you hear a distinct click.

THE CIRCUIT

You need 1x blue ABS plug and a socket, both with as much wire on them as possible. 1x piezo speaker or earphone. 1x 10uf electrolytic capacitor. 1x 3 way 5amp choc-block connector.

Cut the two flexible cables from the plug and socket to about the same length and strip the ends ready to go in the connector. Connect the two with black or black traces into one outer connector (this is the ground connection of the ABS system), connect the remaining two wires also together and insert in the other outer connector along with the positive wire of the electrolytic (they always have markings to indicate +ve or -ve terminal). Push the -ve of the electrolytic into the centre connector. The piezo then connects between the centre terminal and the outer one with the ABS negative terminal.

Below, an ACII diagram (sorry). Wires from ABS plugs on the left, electrolytic plus piezo on the right.

_______oo_______ two none blacks from ABS plug and socket (+ve), plus the +ve of the electrolytic
_______oo_______ piezo, plus -ve end of electrolytic ignor the line entering the (oo) connector on the left.
_______oo_______ two blacks from ABS plug and socket (-ve), plus piezo

The easy way to test your device, is at the N/S front wheel, it is the most easily accessible blue plug. Just pull the plug and socket apart and connect your device in line, jack the front up so you can spin the wheel, turn the ignition to position one and as you turn the wheel you should hear the regular clicks and in the background a buzz.

To use it in earnest

Set it up as above. If you hear no clicks you have either a completely failed sensor of a fault in the loom, or ABS unit, or the ABS fuse. If you hear sharp clicks, then the next stage is to make sure you are hearing a click for every segment. Stand a brick (or similar) vertical very close to the tyre. Rotate the wheel very slowly and each time you hear the click, put a chalk mark next to the brick. If all is good, you should end up with a series of chalk marks, perfectly evenly spaced around the tyre - someone mentioned around 46, but perhaps someone could confirm the correct number (46 ons and 46 offs)? Note there will be two slightly different clicks for each segment, an on click, then an off click.

If any are missing, you have a faulty with the magnetic wheel part, or possibly the sensor to far from the wheel to pick it up. Always worth checking with this gadget if you have replaced a sensor anyway.

Copyright warning

This gadget took me some time and effort to devise and test. It is my copyright, my intellectual property. You are most welcome to make a copy of it for your own use, but you are certainly not welcome to reproduce it for commercial purposes without paying me a suitable fee. I have had my ideas stolen before.

Please note that this circuit can be used for other cars, but it will only work if the system uses Hall Effect sensors.

The general idea. I've used a very old two ear piezo earphone. The capacitor is not an electrolytic, its a not polarity sensitive, but electrolytics are much cheaper if you need to buy one.





The detail of the connections.



Testing a sensor without fitting it in the hub

With the above bit of diagnostic kit you can test a sensor prior to fitting in the hub using the following procedure....

Plug the above kit into the ABS loom plug, plug the suspect sensor into the remaining socket, turn the ignition on and check the ABS warning light goes out. The warning light extinguishing, proves the sensor is basically sound, but it might still fail the following test...

Moving a small, but strong magnet back and forth near the sensor should cause a click in the headphones at about 20mm distance both on the approach and return. It only works with the magnet near to the side of the sensor, not the end. A suitably strong magnet is a 'magnet on a stick', as sold for picking up dropped nuts and bolts from awkward places.

After market sensors

Some report problems with after market sensors not working or giving trouble later. One suggested fix is to adapt the mount in the hub, or the sensor, to allow it to protrude further into the hub, but the above will at least allows you to prove whether the sensor basically works or not, prior to fitting.

[rrobson]

Good luck in constructing the unit, they will be an invaluable aid for many members

[HarryM1BYT]

Absolutely no reason why it shouldn't work. Same idea, just look for the voltage change as `each segment goes past the sensor.

[sworks]

I have a break out box with a variable resistor, dial in the correct resistance and fit in place of the sensor and then you can check if the car passes the self test or the code clears. Not as good as looking at current data but a quick rough and ready test

[HarryM1BYT]

Originally Posted by sworks

I have a break out box with a variable resistor, dial in the correct resistance and fit in place of the sensor and then you can check if the car passes the self test or the code clears. Not as good as looking at current data but a quick rough and ready test

That would be useful for cases where it failed the initial before you move diagnostics.

For the less well informed, there are two diagnostic stages to the ABS..

1. When you first switch the ignition on and the ABS light comes on, where it does a rough check to prove it has a basic connection to the sensors. If it has, the ABS light extinguishes.

2. Stage two is a continuous check, which comes into play when you first rise above a low speed, where it expects to see a series of pulses from all four sensors. If a sensor fails to provide the pulses or misses any pulses, the light comes back on and the ABS is disabled until the ignition is next cycled.

[HarryM1BYT]

Just be aware, that this design will only work when the sensor is an Hall Effect type - not the coil and magnets type. It relies upon the sudden switching of Hall Effect sensors to produce the click.

The coil type produce a slow rise and fall sinusoidal output, best tackled with a scope.