Diy ABS Tester (Which Resistor)

[Best_of_British]

New project has ABS light on constant from start. I think this means it is failing the fist static test, so I want to start with checking the sensors. Speedo works, so I am assuming front driver is ok (looks original stamped BMW). Passenger front looks brand new and Ebay special, this is the one I want to test first.

I have heard about using an old socket which I have, but I need to know which resistor to buy. If anyone could point me in the right direction much appreciated.

[DMGRS]

Our cars use a Hall Effect sensor, so I'm not sure you can use a resistor? I could be wrong, however.
I plugged a new ABS sensor in which wasn't in the hub, and it helped me find the faulty sensor.

[T-Cut]

I found this in my notes. Not mine, but credit to whoever it was (?)

1. Turn ign on wait 10 seconds
2. Turn ign off
3. Unplug OSF sensor (or all sensors*)
4. Turn ign on, wait 10 seconds.
5. Turn ign off.
6. Reconnect sensor.
7. Turn ign on. If light does not go out - you have a faulty sensor. If light does go out you have a faulty reluctor/ bearing. This will be confirmed by the light coming back on after you have driven a few yards.

* This is in case there are two or more faulty sensors.
A working speedo means OSF is OK.
If cruise control works the NSF sensor is OK.

Details on a home made ABS test kit here: http://www.the75andztclub.co.uk/foru...d.php?t=192924

You may be thinking about sensor resistance values. This note (also from HarryM1BYTE) on the Club forum discusses it. http://www.the75andztclub.co.uk/foru....php?p=1765137

TC

[HarryM1BYT]

I doubt, but have not bothered to test if a resistor will fool the system. Which is why I went to the trouble of developing a plug in tester. The details of which you can find linked to in my sig. below...

[Best_of_British]

Many thanks for replies, just snatched a quick hour working on it. After following T-Cuts advice I managed to get the light to stay off. I went through several cycles of starting and turning off the car, resulting in the ABS light staying off. Am I right in thinking that all sensors are passing the static test and must be ok?

Next test, drove 7 seconds down the road and the light came back on and is still on after a few stop start cycles. Does this narrow it to a hub reluctor ring or could it be that the new Ebay sensor has not been fitted with correct gap or debris cleaned properly?

Is the ECU in the clear as I got the light to stay off on the static test or should I be taking the battery box off and looking at the connectors on ABS ecu.

Any advice on narrowing it down to which reluctor ring?

On the resistor issue to fool the static test to check, I have found an old post on here mentioning 1.50K 1% resistor but as no one seems to have took this method up it is probably a non starter.

[DMGRS]

I've had many a duff eBay sensor - had 2 myself, and a good few of my customers have had to replace them for similar issues. Some appear 'dead' whereas some give spurious readings.

Saying that, if you've replaced the sensor due to other issues, it could well be a bearing. Thankfully they're quite cheap.
Front bearings are here: 75/ZT Wheel Bearing - Front

[HarryM1BYT]

Originally Posted by Best_of_British

Next test, drove 7 seconds down the road and the light came back on and is still on after a few stop start cycles.

The light going out means it passed the initial diagnostics, where the ABS 'sees' all four sensors connected.

If it then fails once the car moves, you need to try my diagnostic unit to narrow it down further, or get it on a T4.

Once moving, it expects to 'see' 46 pulses evenly spaced, per revolution of each individual wheel, if any are missing or irregular - a fault is assumed.

I would be very suspicious of the Ebay special. Cruise I think uses that sensor, does cruise drop out if you have it fitted?

Some have reported problems with some sensors being mounted to far away from the ring and had to find ways to reduce the distance.

[Mike Noc]

Interestingly, if the sensor is a bit too far from the magnetic reluctor ring then the speedometer can still work but the ABS alarm comes on.

Had that on a rear sensor that was missing the odd random segment but only at very low speeds. As I have an extended cable I plugged it into the OSF, gave the wheel a spin, and the speedo read perfectly.

Best to check that each sensor sees every segment with a multimeter and rotating the wheel segment by segment.

[okenora]

Does this narrow it to a hub reluctor ring or could it be that the new Ebay sensor has not been fitted with correct gap or debris cleaned properly?

Could be either, both or neither......

Is the new sensor on the front or rear?
If front then left or right?
if left , do you have cruise and does it still work? if it does then likely that corner is ok.
if right, does your speedo work smoothly and accurately? if it does then likely that corner is ok

TESTING ABS

Get a multimeter and a stick of chalk.
Connect the meter to each sensor in turn as detailed here and perform the following...

Jack the wheel so it is free to turn, chock wheels where needed for safety as handbrake will be off to do the rears.
Rotate the wheel while watching the meter for a voltage change, at each change place a chalk mark at the top of the tyre. You should have a nice even pattern after one rotation.

If bits/marks are missing.....

If it is the same mark(s) missing every time it is more likely the reluctor ring or dirt on it.
If it is a different one every time it is more likely the sensor spacing

A T4 will quickly identify the wheel(s) at fault but afaik will not differentiate easily between a failing/damaged reluctor and a badly spaced sensor.

BMW scanner will also identify the wheel at fault.

[Best_of_British]

Time to get the multimeter out then, drivers front ABS sensor is original, but the speedo works fine so I will assume this is ok. No cruise fitted and passenger front sensor appears to be a new cheapie, so I will start here.

Just to make sure I understand this right:

1) Set multimeter to 20v DC
2) Unplug blue connecter on Passenger Front
3) Crocadile clip on + red probe clipped on to a map pin
4) Pin pushed into Red sensor wire pin on blue connector.
5) Black probe to earth on car
6) Jack wheel of ground
7) Slowly spin wheel counting how many times voltage switches from 0.7 to 1.7
8) Chalk up on wheel each switch and the result should be and even 46 chalk marks?

If this is correct I will try it tomorrow on NSF then rears and report back.

Chalk is cheaper than £35 scanner.