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[Doctor Gollum]

Position of the sensor head both in depth and orientation will affect the magnetic field and thus the reading and operation of the ABS.

The sensor magnet should be oriented parallel to the reluctor face.

Another consideration is that the number of notches on the reluctor ring face is identical to the original and likewise the magnetic tip of an aftermarket sensor.

The owners manual should give the operating parameters of the ABS as a system as it doesn't function across the entire speed envelope.

[bkorven]

Position of the sensor head both in depth and orientation ...

The sensor magnet should be oriented parallel to the reluctor face.
...

Orientation mentioned first, as in the rotation against the teeth in addition to just as in how parallel it is, as mentioned afterwards?

I wonder if by rotating the sensors, I am affecting how parallel they are towards the reluctor rings, and thus affecting the signal strength. Which also makes me wonder if new steering knuckles would solve my problem. But I highly doubt it.

Right now the sensors are barely touching the rings, so the depth should be excluded as a possible cause.

Thinking out loud:
Are the mounting surfaces for the sensors om my steering knuckles not flat/even enough? Is there a reasonable probability that this problem could be exactly the same on both sides?

[bkorven]

I've only played with Carlton/Senator ABS, not Omega B, and it might be different - but.....

There is no ground on the sensors. The two sensor wires are differential all the way to the control unit. Infact the resistance to ground of both terminals is many hundreds of K-ohms. If either terminal is somehow shorted to ground, the ABS fault light comes on.

As I say - on the Carlton/Senator.

Thank you! That is valuable information.

I have measured the resistance of the terminals to 6.8M Ohm on both sides, and I assume that reading is OK.

[Doctor Gollum]

Position of the sensor head both in depth and orientation ...

The sensor magnet should be oriented parallel to the reluctor face.
...

Orientation mentioned first, as in the rotation against the teeth in addition to just as in how parallel it is, as mentioned afterwards?
Yes

I wonder if by rotating the sensors, I am affecting how parallel they are towards the reluctor rings, and thus affecting the signal strength. Exactly this. Which also makes me wonder if new steering knuckles would solve my problem Waste of money. But I highly doubt it.
The new bearing assembly and the sensor could both be the cause, especially if cheap parts have been used.
Right now the sensors are barely touching the rings, so the depth should be excluded as a possible cause.

Thinking out loud:
Are the mounting surfaces for the sensors om my steering knuckles not flat/even enough? Is there a reasonable probability that this problem could be exactly the same on both sides?

To your first point, I did suggest this when you first raised the question 

To your last point, it's possible that the new sensors are a cheap impression of the genuine article and are totally out of shape. In fact, because you ended up fitting them clocked away from the bolt holes, the chances are that they are basically junk.

A genuine sensor should fit into the knuckle precisely and it's extremely unlikely that the hole in the knuckle is distorted.

[Enceladus]

The best deal I could find on new sensors was from USA. These sensors was specified to fit 1997 Cadillac Catera, but the OEM part number (90509421) matched. Could this be an issue?..

Were the Cadillac ABS sensors genuine GM or were they third party?

[LC0112G]

I've only played with Carlton/Senator ABS, not Omega B, and it might be different - but.....

There is no ground on the sensors. The two sensor wires are differential all the way to the control unit. Infact the resistance to ground of both terminals is many hundreds of K-ohms. If either terminal is somehow shorted to ground, the ABS fault light comes on.

As I say - on the Carlton/Senator.

Thank you! That is valuable information.

I have measured the resistance of the terminals to 6.8M Ohm on both sides, and I assume that reading is OK.

Yes, that sounds about right.

The sensors are called variable reluctance sensor. Their output signal amplitude is a function of both RPM and clearance. You seem to be saying that by rotating the sensor things get better/worse. Note that the clearance is important - if the sensor is too close to the reluctor ring then it'll generate too high voltage, and this can upset the control unit. Rotating the sensor will reduce the amplitude as the 'blade' of the sensor becomes mis-aligned with the teeth on the reluctor ring..

So check the clearance between the tip of the sensor and the reluctor ring on the wheel bearing. I don't know what it is supposed to be, but I'd expect something like 1mm-2mm. You say up thread that it is (almost?) touching. That isn't correct. If it is, then the sensors are wrong but you might be able to correct it by putting shims in between the sensor and the steering knuckle.

[bkorven]

Position of the sensor head both in depth and orientation ...

The sensor magnet should be oriented parallel to the reluctor face.
...

Orientation mentioned first, as in the rotation against the teeth in addition to just as in how parallel it is, as mentioned afterwards?
Yes

I wonder if by rotating the sensors, I am affecting how parallel they are towards the reluctor rings, and thus affecting the signal strength. Exactly this. Which also makes me wonder if new steering knuckles would solve my problem Waste of money. But I highly doubt it.
The new bearing assembly and the sensor could both be the cause, especially if cheap parts have been used.
Right now the sensors are barely touching the rings, so the depth should be excluded as a possible cause.

Thinking out loud:
Are the mounting surfaces for the sensors om my steering knuckles not flat/even enough? Is there a reasonable probability that this problem could be exactly the same on both sides?

To your first point, I did suggest this when you first raised the question 

To your last point, it's possible that the new sensors are a cheap impression of the genuine article and are totally out of shape. In fact, because you ended up fitting them clocked away from the bolt holes, the chances are that they are basically junk.

A genuine sensor should fit into the knuckle precisely and it's extremely unlikely that the hole in the knuckle is distorted.

The signal strength was unaffected by installing the new bearing assemblies, so they are not the cause.

The sensors might be crap. In that case, I consider myself to have been scammed. The seller could honestly just as well have sent me an empty box, and it wouldn't be any different from receiving a dysfunctional product. In fact, that would actually have saved me time, money and hassle. Sigh... let's hope it's not the sensors. I don't know how to confirm that without committing to buying new ones.

[bkorven]

The best deal I could find on new sensors was from USA. These sensors was specified to fit 1997 Cadillac Catera, but the OEM part number (90509421) matched. Could this be an issue?..

Were the Cadillac ABS sensors genuine GM or were they third party?

The sensors are of the brand "Holstein", part number "2ABS1206". I don't know for sure what brand the sensors has from factory.

[bkorven]

I've only played with Carlton/Senator ABS, not Omega B, and it might be different - but.....

There is no ground on the sensors. The two sensor wires are differential all the way to the control unit. Infact the resistance to ground of both terminals is many hundreds of K-ohms. If either terminal is somehow shorted to ground, the ABS fault light comes on.

As I say - on the Carlton/Senator.

Thank you! That is valuable information.

I have measured the resistance of the terminals to 6.8M Ohm on both sides, and I assume that reading is OK.

Yes, that sounds about right.

The sensors are called variable reluctance sensor. Their output signal amplitude is a function of both RPM and clearance. You seem to be saying that by rotating the sensor things get better/worse. Note that the clearance is important - if the sensor is too close to the reluctor ring then it'll generate too high voltage, and this can upset the control unit. Rotating the sensor will reduce the amplitude as the 'blade' of the sensor becomes mis-aligned with the teeth on the reluctor ring..

So check the clearance between the tip of the sensor and the reluctor ring on the wheel bearing. I don't know what it is supposed to be, but I'd expect something like 1mm-2mm. You say up thread that it is (almost?) touching. That isn't correct. If it is, then the sensors are wrong but you might be able to correct it by putting shims in between the sensor and the steering knuckle.

I estimate the distance to be somewhere around 0.2-0.3 mm at the moment. But the signal is too weak, and not the other way around. I don't know what the voltage should be specifically for the Omega, but reading online it seems to usually be between 0.5-1 V at 2 RPM of the wheel. I get ~50mV when the sensors are mounted in their intended position as from factory, and I can manage to get ~200mV when I rotate them.

The stronger I manage to get the signal (by rotating), the better the behaviour of the ABS.

The reason ABS is activated is likely due to the signal being too weak to be registrated by the ECU, so that it is interpreted as the wheels locking up.

[LC0112G]

Sounds to me like the wrong sensors. EPC doesn't show the OEM part number, but most braking stuff on large Vauxhall/Opels is Bosch. Certainly is Bosch on Carlton/Senator.

I've never heard of Holstein (except as a cheap Beer here in the UK, and as a state in Germany)

[cam.in.head]

on all the evidence this would appear to be the problem. after all everything was ok untill you replaced the sensors. other parts worked on the original sensors .when you said you had got new ones i think we assumed you had found oem ones albeit for the caddy.

[Doctor Gollum]

Sounds to me like the wrong sensors. EPC doesn't show the OEM part number, but most braking stuff on large Vauxhall/Opels is Bosch. Certainly is Bosch on Carlton/Senator.

I've never heard of Holstein (except as a cheap Beer here in the UK, and as a state in Germany)

They are a Florida based reseller of third party manufactured parts.

I suspect that these sensors were purchased on price. And at risk of repeating myself. Again. If a part doesn't bolt straight in and/or appears different in anyway to the factory original, then it is unlikely to function correctly. Especially if it's electrical.

Buy a pair of genuine sensors, fit them and report back.

[Doctor Gollum]

Position of the sensor head both in depth and orientation ...

The sensor magnet should be oriented parallel to the reluctor face.
...

Orientation mentioned first, as in the rotation against the teeth in addition to just as in how parallel it is, as mentioned afterwards?
Yes

I wonder if by rotating the sensors, I am affecting how parallel they are towards the reluctor rings, and thus affecting the signal strength. Exactly this. Which also makes me wonder if new steering knuckles would solve my problem Waste of money. But I highly doubt it.
The new bearing assembly and the sensor could both be the cause, especially if cheap parts have been used.
Right now the sensors are barely touching the rings, so the depth should be excluded as a possible cause.

Thinking out loud:
Are the mounting surfaces for the sensors om my steering knuckles not flat/even enough? Is there a reasonable probability that this problem could be exactly the same on both sides?

To your first point, I did suggest this when you first raised the question 

To your last point, it's possible that the new sensors are a cheap impression of the genuine article and are totally out of shape. In fact, because you ended up fitting them clocked away from the bolt holes, the chances are that they are basically junk.

A genuine sensor should fit into the knuckle precisely and it's extremely unlikely that the hole in the knuckle is distorted.

The signal strength was unaffected by installing the new bearing assemblies, so they are not the cause.

The sensors might be crap. In that case, I consider myself to have been scammed. The seller could honestly just as well have sent me an empty box, and it wouldn't be any different from receiving a dysfunctional product. In fact, that would actually have saved me time, money and hassle. Sigh... let's hope it's not the sensors. I don't know how to confirm that without committing to buying new ones.

You missed my point re the bearings... If the reluctor teeth are different in number, size or shape to the factory originals, then they will cause an error even if the signal strength is consistent. The ECU will be looking for a specific number of teeth and if there's a mismatch between wheels or axles, then it won't function correctly. The sensors are a different issue, but both will cause faulty performance, and you've already admitted thet the sensors don't fit as you can't fit the retaining bolts. Which means that the sensors are free to move both rotationally and in/out along the casting. They're bolted for a reason.

[dave the builder]

I've only played with Carlton/Senator ABS, not Omega B, and it might be different - but.....

There is no ground on the sensors. The two sensor wires are differential all the way to the control unit. Infact the resistance to ground of both terminals is many hundreds of K-ohms. If either terminal is somehow shorted to ground, the ABS fault light comes on.

As I say - on the Carlton/Senator.

Thank you! That is valuable information.

I have measured the resistance of the terminals to 6.8M Ohm on both sides, and I assume that reading is OK.

Yes, that sounds about right.

The sensors are called variable reluctance sensor. Their output signal amplitude is a function of both RPM and clearance. You seem to be saying that by rotating the sensor things get better/worse. Note that the clearance is important - if the sensor is too close to the reluctor ring then it'll generate too high voltage, and this can upset the control unit. Rotating the sensor will reduce the amplitude as the 'blade' of the sensor becomes mis-aligned with the teeth on the reluctor ring..

So check the clearance between the tip of the sensor and the reluctor ring on the wheel bearing. I don't know what it is supposed to be, but I'd expect something like 1mm-2mm. You say up thread that it is (almost?) touching. That isn't correct. If it is, then the sensors are wrong but you might be able to correct it by putting shims in between the sensor and the steering knuckle.

I estimate the distance to be somewhere around 0.2-0.3 mm at the moment. But the signal is too weak, and not the other way around. I don't know what the voltage should be specifically for the Omega, but reading online it seems to usually be between 0.5-1 V at 2 RPM of the wheel. I get ~50mV when the sensors are mounted in their intended position as from factory, and I can manage to get ~200mV when I rotate them.

The stronger I manage to get the signal (by rotating), the better the behaviour of the ABS.

The reason ABS is activated is likely due to the signal being too weak to be registrated by the ECU, so that it is interpreted as the wheels locking up.

Have you ground or filed the surface that the sensor sits on ,to make the sensor CLOSER to the reluctor ring 
the surface looks way too flat and clean compared to the rest of the casting in your image


have you tried shimming the sensor out ,to see how that effects the signal 
though i suspect the after market sensors may be the issue .

[ronnyd]

Sounds to me like the wrong sensors. EPC doesn't show the OEM part number, but most braking stuff on large Vauxhall/Opels is Bosch. Certainly is Bosch on Carlton/Senator.

I've never heard of Holstein (except as a cheap Beer here in the UK, and as a state in Germany)

Also where much of your milk emanates from, moo.