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16

Omega General Help / Re: ABS-light constantly on after replacing front ABS/wheel speed sensors

« on: 28 October 2023, 15:13:47 »

Incidentally, what hubs did you fit? Whilst they are both have 48 teeth, they look very different in your photo. The new reluctor face looks to be off centre.

These are the hubs I ordered: https://www.autodoc.co.uk/ridex/8054400
And these are the hubs I received, which is not what I ordered: https://www.buycarparts.co.uk/esen-skv/18164200

I suspect that one manufacturer produces parts for several brands, and the only difference is the logo on the box.

17

Omega General Help / Re: ABS-light constantly on after replacing front ABS/wheel speed sensors

« on: 28 October 2023, 14:25:21 »

Both the frequency AND amplitude of the sensor output will increase with RPM. You say you are measuring at 2 RPM. Assuming you're using 235R45x17 tyres, the rolling circumference is 79.57 inches (2021mm). 2 RPM is 120 revs per hour, which is therefore 9548 inches per hour, which is only 0.15 miles per hour.

I don't think the ABS is supposed to work at all below 5mph. Therefore the voltages you are seeing from the sensors are not representative of what you should see if the car is travelling at > 5MPH (8 Km/h).

Your 50mV at 2RPM might be correct - Try it again at a more realistic 200RPM (15 MPH), you should get a much larger signal - probably 20-50 times larger. Remember the ABS needs to work all the way up to above top speed (say 2000RPM/150MPH) so the signal can be massive at that speed. If you adjusts the sensors to give large signals at very low speeds, then at normal/high speed you can overload the ABS inputs.

I've got some old Carlton hubs in the lockup, still with the ABS sensors fitted. I'll dig them out tomorrow and measure them up for clearance. 0.2-0.3mm sounds way too close to me.

I'm comparing my voltage at 2 RPM to what others have measured at that same speed, so what voltage the sensors generate at higher speeds is not really of relevance for that matter. I'm expecting 0.5V-1V at 2 RPM, but I'm measuring much lower than that at 2 RPM.

Overload the ABS-inputs, as in causing damage, or as in disrupt the function? I assume there is binary switching inside the ECU, for a threshold value of the signal. In that case, the signal just needs to be strong enough, and all that matters is frequency/consistency of the signal. I could be (and probably am) wrong.

I am convinced that 0.2-0.3mm is a shorter distance than what it was originally, but I'm not convinced the distance can be too short. I also still believe my signal is too weak.

Either way, I'm grateful for you for taking the time to check it out.

18

Omega General Help / Re: ABS-light constantly on after replacing front ABS/wheel speed sensors

« on: 28 October 2023, 13:21:50 »

Which just goes to show that the sensors are wrong.

You might try fitting them in the correct position, and see if the driveability improves.

The sensors might work electrically but the information they are sending to the ABS ECU is clearly not right.

Might indicate that they are wrong. Not 100% certain of that.

I have tried fitting them in the correct position. It gets worse, and the ABS-light comes on again.

I agree with you about that, the information they are sending is definitely not right.

19

Omega General Help / Re: ABS-light constantly on after replacing front ABS/wheel speed sensors

« on: 28 October 2023, 13:20:08 »

Thanks for all the input, from all of you! I really appreciate it.

It seems highly likely that the sensors are bad, after all. I actually did not know the sensors I had ordered were not genuine OEM. The brand of the ones I ordered was pretty well hidden under an "extra info"-tab that needed to be opened to show. It would have been better if I had provided you with information about the manufacturer early on, ofcourse.

I'll order new ones, and will report back with the result.

The problem now is that the only sensors that seem reasonable, that I seem to be able to get online, are of brand "Vemo", model "V40-72-0472". No genuine sensors anywhere to be found. Just alot of other shady "beer"-named ones and similar.

I think I'll just do it the old way, and give my local Opel-dealer a call on Monday.

20

Omega General Help / Re: ABS-light constantly on after replacing front ABS/wheel speed sensors

« on: 28 October 2023, 13:11:12 »

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 .

Yes, I have filed the surface that the sensor sits on. It was an attempt to make the signal stronger... and a successful one at that 

In my desperate troubleshooting I saw a possible cause of the problem that corrosion had increased the clearance.

I have tested the signal with a larger distance from the reluctor ring, yes. The signal gets weaker, as expected.

21

Omega General Help / Re: ABS-light constantly on after replacing front ABS/wheel speed sensors

« on: 28 October 2023, 13:07:08 »

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.

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.

Oh okay, I see. If the reluctor teeth would be that different from the stock ones, I'd find it startling to be honest. Am I naive to believe that parts that are sold should work? Anyways, I'm quite sure the bearing assemblies are OK. The dimensions and number of teeth was stated, and was the same for all different brands of bearing assemblies. I suppose it's harder with sensors, since they don't really state the number of windings inside them, or other such detailed information about the performance.

Although I guess it doesn't have any greater relevance to the discussion, just to clarify; the aftermarket sensors does fit perfectly. The signal is just too weak, and by rotating them it gets stronger.

To Dave's last... That surface just looks clean, but the sensor is clearly clocked wrong. Ergo it is wrong and won't work correctly.

The magnet is, or should be, the size of the teeth on the reluctor. If it is clocked even a few degrees it will cover more than one tooth and therefore not pick up every space. Effective this fools it into see less teeth and therefore presuming the wheels are locking up. If the rear sensors are reading correctly then the ABS over reacts even more due to the fact that it thinks the front wheels are rotating at half the speed.

Undo everything you have done with actual genuine sensors and the system will work perfectly.

While your reasoning with the magnet seeing more than one teeth at the same time in a rotated position sounds reasonable, the ABS-behaviour was actually improved by rotating the sensors away from the original position. I could not tell the frequency of the signal was affected, either.

22

Omega General Help / Re: ABS-light constantly on after replacing front ABS/wheel speed sensors

« on: 27 October 2023, 22:31:19 »

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.

23

Omega General Help / Re: ABS-light constantly on after replacing front ABS/wheel speed sensors

« on: 27 October 2023, 22:24:53 »

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.

24

Omega General Help / Re: ABS-light constantly on after replacing front ABS/wheel speed sensors

« on: 27 October 2023, 22:22:16 »

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.

25

Omega General Help / Re: ABS-light constantly on after replacing front ABS/wheel speed sensors

« on: 27 October 2023, 10:02:30 »

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.

26

Omega General Help / Re: ABS-light constantly on after replacing front ABS/wheel speed sensors

« on: 27 October 2023, 09:54:52 »

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?

27

Omega General Help / Re: ABS-light constantly on after replacing front ABS/wheel speed sensors

« on: 26 October 2023, 21:07:43 »

Thanks for all the replies.

Unfortunately, the problem persists. Now, though, I am almost completely certain it is all about signal strength.

The wheel hub assemblies were replaced in the front. And they were torqued to 320 Nm, according to specification New reluctor rings gave no improvement.







By rotating the sensors inside their mounting hole on the steering knuckle, and thus varying the signal strength for some reason, I have found that at what speed ABS is activated seems directly proportional. "Sweet spot" leads to the ABS activating just before coming to a stop, at perhaps 5 km/h. The closer I rotate the sensors back to their original position, the higher the speed at which ABS starts intervening. And with the sensors in their original position, ABS-light also comes on.

Note that front left and front right sensor seem to perform identically.

So my reflections right now are:
 - Could the signal be weak due to bad connection to ground?
 - Do front left and front right wheel speed sensors share ground?
 - Why would this problem arise after replacing front suspension along with new sensors?

This is the only ground I've found under the hood. Can someone confirm if this could be where the sensors ground?:




I guess my next step will be to check wiring, and I'll also test supplying a new temporary ground.

28

Omega General Help / Re: ABS-light constantly on after replacing front ABS/wheel speed sensors

« on: 02 October 2023, 17:29:13 »

not having a front one to hand to look at but i assume the design is physically similar to the rears .the sensor 'pick up area' is exactly in line with the mounting lug.i wonder if replacements are identical or could be off centre in any way ? explaining the rotation difference or the body depth is in any way slightly different.?   as mentioned,replacing (or at least checking/cleaning) the toothed ring would at least make that part eliminated.

I could not tell a difference between the replacement sensors and the ones I had before. The thought has crossed my mind, that there could be a slight difference, although the OEM number matches.

Either way, I am very excited to replace the hubs and perform new measurements. They were ordered today.

By the way; Haynes manual states the hub nut to be torqued to 320 Nm. That sounds extremely high. Thoughts on this? My biggest torque wrench goes to 210 Nm, and I'll probably turn it some extra degrees afterwards and be happy.

29

Omega General Help / Re: ABS-light constantly on after replacing front ABS/wheel speed sensors

« on: 01 October 2023, 15:39:05 »

brilliant .glad you sorted it.
and also its nice for someone like yourself to come on afterwards and say the problem has been fixed.so many forums give helpfull advice to people and you never hear a word after !

Thank you! Hehe, I've several times found myself reading similar threads on different topics where I have been dying to know about the outcome and what fixed a problem. I'm grateful for everyone trying to help out, so to come back with answers to what was wrong is the least I can do.

30

Omega General Help / Re: ABS-light on after replacing front ABS/wheel speed sensors (Solved)

« on: 01 October 2023, 15:30:53 »

The ABS light went out as soon as I started the car and got rolling. What I find odd though, is that the signal gets stronger by rotating the sensor out of its intended alignment in the hole. While turning the sensor in the hole, I would find a sweet spot where I left it at. See pictures below, for original position and the position with stronger signal (~50mV AC vs ~200mV AC). This orientation of the sensor means that I can't attach it with the bolt, but it sits very tightly in the hole and won't move. It was the same on both sides.


Original position


Sweet spot

So make sure the sensors are clean and that the gap to reluctor ring is sufficiently small!

I've had exactly this problem and found exactly the same with a pattern sensor (Vemo). Wheel bearing had also been replaced (as you know reluctor part of bearing / hub assembly) at the same time. the 'sweet spot' worked fine but obviously can't be fixed as the bolt hole didn't line up. I managed to source a brand new, old stock genuine GM sensor from Germany and it's been fine ever since. 

That is very interesting! The signal on my car is still too weak in its original orientation, and I suspect the reluctor rings to be bad.

Will replace, and I'll get back with the results!