Datatek said:

Never done one, but I believe the ABS ECU is Plug & Play.
Sensor resistance may not be a good guide to function.

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N5Fav said:

Resistance checking a wiring loom tells you very little apart from the fact that wire runs through from one end to the other, you can have 25 strands broken in a length of wire, and the remaining two strands that are connected will show zero resistance.

What you need to do is load the wiring loom with a voltage, and then check the volt drop.
To do this, disconnect both ends of the loom, supply 12v at one end of the cable you are checking,and put a load at the other end - a 60w headlamp bulb is ideal for this. Once this is connected up and the bulb is lit you check the volt drop. To do this you measure the volt at each end of the wire you are measuring, you will probably have to use a good length of wire to go from one end of the loom to the other to extend your volt meter leads.

What you are actually measuring is the amount of voltage that wont go down the wire, ideally you want less than 0.25 volts showing on your volt meter. Certainly any more than half a volt and you have a problem. As your reported problem is a possible short circuit, leave the volt meter in the wire you have just tested, and then check for voltage in all the other wires in the loom.

It may well be the ABS unit that is at fault, but check it is worth spending a bit more time checking the loom properly first.

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Rick-the-Pick said:

Those ABS faults are a pain. It's always the near side rear that causes complaint.
Have you checked the passenger footwell kickpanel connectors for corrosion?

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Owen89VSE said:

The 1.6v held when i did the loom test
Everything seems corrosion free....
Does anyone know the rough voltage that should be read on the live data for the wheels when you spin them (slowly)?

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Saint.V8 said:

Thought the Sensors were Hall Effect sensors??

The ECU gives a reference voltage to the sensor and as the toothed wheel passes the sensor, the effect of the change in magnetic field (Hall Effect) changes the return voltage!!

This will give a alternating wave pattern of the return voltage!

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N5Fav said:

If it's a Hall type sensor then there is no point in testing the sensor for resistance, in fact you could damage the sensor trying to test it.
I would expected though on a vehicle of this age it would have inductive type sensors fitted. (No doubt somebody with more specific RR knowledge can correct me on this).

If it is inductive type sensor, (which seems to be backed up by the fact that there is a specific resistance value available), then as the wheel rotates this produces an AC waveform. The ABS ecu translates that information into a road wheel speed and compares it with the other road wheel speeds.

Now here it can get interesting, effectively the ECU is counting how many times the AC waveform is passing 0v - (ie going from +v to -v as its AC current remember). The ECU is not interested in what the voltage is, as when the car goes faster, a greater voltage is produced by the sensor (a bit like a bicycle dynamo light gets brighter the faster you cycle). This is why there is no data for voltage to/from the sensor available. These voltages will certainly exceed 12v when you are at motorway speeds.


Wammers, I agree that two strands of wire would burn out quickly when it has to light a headlamp bulb. But now your testing has located and proved a wiring loom fault.
I was trying to show and explain that just doing a resistance check on the loom wiring is not a complete test.

HTH and that I've made sense

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A sensor is mounted at each wheel sensing a 60 tooth exciter ring. When the vehicle is in motion the inductive sensors send signals to the ECU.

The front exciter ring is fitted adjacent to the constant velocity joint in each front hub. The rear exciter ring is inside the axle adjacent to the wheel bearing assembly.

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N5Fav said:

If it's a Hall type sensor then there is no point in testing the sensor for resistance, in fact you could damage the sensor trying to test it.
I would expected though on a vehicle of this age it would have inductive type sensors fitted. (No doubt somebody with more specific RR knowledge can correct me on this).

If it is inductive type sensor, (which seems to be backed up by the fact that there is a specific resistance value available), then as the wheel rotates this produces an AC waveform. The ABS ecu translates that information into a road wheel speed and compares it with the other road wheel speeds.

Now here it can get interesting, effectively the ECU is counting how many times the AC waveform is passing 0v - (ie going from +v to -v as its AC current remember). The ECU is not interested in what the voltage is, as when the car goes faster, a greater voltage is produced by the sensor (a bit like a bicycle dynamo light gets brighter the faster you cycle). This is why there is no data for voltage to/from the sensor available. These voltages will certainly exceed 12v when you are at motorway speeds.


Wammers, I agree that two strands of wire would burn out quickly when it has to light a headlamp bulb. But now your testing has located and proved a wiring loom fault.
I was trying to show and explain that just doing a resistance check on the loom wiring is not a complete test.

HTH and that I've made sense

Click to expand...

Owen89VSE said:

Well, I can add to the list that is not the brake pads, hub nut loose/bearings and Hawkeye says each corner is giving a good wheel speed and working as it should.
I am totally lost now.

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