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A generic test method for ABS wheel sensors.
OK, here you go, enjoy!
1. You need to be able to power the sensors from the ABS controller whilst monitoring the dc voltage with a digital multimeter. I do not like the resistance only method. Not only does it not power the sensor, but the leads all the way back to the ABS controller are not tested and you do not know if the controller is providing the correct voltage source.
2. I did not do it but you could remove the plug from the ABS module under the front left side and attach/solder pairs of wires for each wheel sensor if you know what pins they are on then replace the plug.
3. I made a simple 'Y' break out lead which allows the male and female halves of the wheel sensor to be electrically connected whilst jumpering the pair and connecting to a digital multimeter.
4. The Renault connectors use a 2.5mm dia. pin. If you have some copper or brass rod that size you can solder a couple of short lengths on to wires, sleeve over and make a pair of pins which will fit the female connector. 2.5mm house cable is 2.0mm dia. so I used a couple of bits of that tinned with solder to build up to 2.5mm dia. The opposite end needs loops to push over the male pins and you can create those by removing some wire insulation, wrapping the wire around a 2.5mm drill and solder tinning. In the centre you attach a further 2 wires which will connect to your multimeter set on dc voltage for about 10 volts. If you are a Renault whizz you will have broken sensors and harnesses just lying about to cannibalise the wheel sensor connectors from!
5. Remove a road wheel, feel the sensor wire path and find the connector clipped just behind the box frame section. Find the small holes in the cover that slide over the lock clips, insert a jewellers or fine screwdriver under the cover and separate the 2 connectors. I have posted a diagram of what mine look like on my Lag1. Note the view is on the ends and when you connect the 'Y' lead you must make sure the socket to pin connection is the same as if they were mated together.
6. Now attach the 'Y' lead to each connector and tape it to the lower suspension arm. Make sure the pins an loops over pins are twisted so they do not short together. Connect the digital multimeter to the pair of wires. You now have your digital multimeter bridging the sensor which is electrically connected to the ABS controller module.
7. Take the spare wheel out of the boot and mount it on the hub with 2 wheel bolts. Mark the wheel near a bolt hole so you can put it back in the same position later if needed.
8. Take a short length of welding wire and bend it to form a reference in line with the centre of the wheel hub and fixed to the body as shown in my photo. It does not matter where it is fixed, but on the front arches there is a convenient self tapping screw holding down trim. You could even clamp it to the arch return with a mole clamp (on the rears).
9. Get yourself some chalk or wax crayons to mark the tyre wall with.
10. Switch on the ignition (motor not running) and test your setup by rotating the wheel. You should see the voltage on the multimeter change from about 10 volts down to 9 volts. These are the wheel pulses which the ABS controller sees.
11. Inch the wheel until the multimeter shows a voltage high level and make a longish mark on the tyre. This is your starting reference. Now slowly inch the wheel in the same direction each time and watch the voltage drop to the low level and return to the high level. At each high voltage level, make a smaller mark on the tyre. Carefully and patiently repeat all the way around the wheel. Every time you get a high and low voltage, rock the wheel back and forth making sure the resulting position relative to the tyre mark you made is repeatable.
12. If your sensor wiring back to the ABS controller is ok you will be getting voltage pulses like I have shown in my diagram. If you do not get those voltages or there are no pulses then either the bearing target magnet is on the wrong side of the bearing or the wiring or ABS controller is faulty. If you suspect the bearing target is not there, remove the sensor and move it towards a small magnet to check for a voltage change. If none and the voltages to it are correct then the sensor itself is faulty.
13. Carefully inspect the marks you made all the way around the tyre. The gaps between your marks must be equal. If they are not, then you have defects in the bearing target magnet and the ABS will fault. My tire is marked with yellow crayon in 2 positions where the target ring was missing magnets.
14. Now you replace the spare with the roadwheel you took off and move on to the next wheel ( now you will understand why you used the spare!).
15. Connect up your 'Y' lead to the next wheel sensor and align your reference wire fixed on the body to your start mark which corresponds to a voltage high point on the multimeter. bend the refernce pointer a little if necessary. now you repeat the excercise but this time you just need to make sure each mark aligns with the peak voltage point and that it is reliable all the way around.
16. You repeat the procedure on the remaining 3 wheels looking carefully for voltage peaks or lows that are missing or 'flaky/intermittent'. You can even put a refernce mark on the bearing rear BUT NOT THE SENSOR RING itself, so you can have a closer look with a magnifying glass. Chances are you will find some kind of 'ding' in the target - possibly caused by road debris thrown up underneath. Now if you find any of the others have more or less peak voltage points per wheel revolution, you have a big problem because they all must be the same. Perhaps you got a bearing and they put a target magnet on it which was not for your vehicle?
17. This test will check sensor problems at slow speeds, but if your ABS lights are clear until you hit motorway speeds, then that becomes a trickier frequency related problem to find. Usually this problem would be caused by too much air gap between the sensor and target, but equally a target with diminishing magnetism could give the same fault.
18. I will not cover this here, but essentially the road wheels need to be run at speed in gear whilst looking on an oscilloscope to determine if pulses are missed. This is possible on the front but not so easy to do for the rears unless you have a rolling road. Just make sure the sensors are clean with a small air gap to the target and the target itself is clean.
Finally, remember that removing a hub, carrier, bearing and refitting new is a long process so be ultra careful. Only buy FAG or SKF bearings which come in protective packaging for the target ring and notes telling you which side it is on. If your wheel bearing with target ring is coming from an auction website and does not have that extra protection for the target, do not buy it! Make sure your workshop pressing in the new bearings knows they must not damage the target in the press. When you refit a hub with a new bearing, pull the lower suspension arm as low as you can get it with a rope tourniquet so the ball joint thread is well clear. You should have fitted spring compressors at stage 1 before removing the old hub to keep the driveshaft horizontal and be extra careful using a wrench on the lower ball joint nut which is very close to the bearing target.
In my photos I have included a photo of an old bearing where I have easily lifted and broken off a section of the target magnet so you can see just how thin it is. If only one magnet section out of the total of 44 (?) in the target is damaged, then your bearing is useless and you cannot buy replacement targets to stick on yourself (shame).
Last edited by hondo; 15th August 2015 at 05:56 PM.
Reason: Perceived CC image removed