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[bkorven]

As I replaced suspension parts on my 1998 Omega B 2.0 16V, I tried removing the front ABS/wheel speed sensors. They broke, on both sides... and I learned that you simply do not remove them.  Note that the ABS-light was not on before the sensors were replaced.

After having installed everything, along with the new sensors, the ABS-light went on after having driven a few hundred meters.

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?..

Measuring the sensors with a multimeter shows a resistance of ~1520 Ohm, on both sides. The sensors both react to waving a magnetic material past them. Rotating the wheel hubs slowly results in a voltage of 0.1-0.2 VDC, both sides, but it does not seem consistent.. I do not get any reading measuring ADC.

I have tried thoroughly cleaning the teeth on both wheel hubs.

I have tried connecting an ELM327 OBD, but it tells me that there is no communication with the ECU (the ELM327 works with other cars). I also tried getting codes by shorting pin 5 & 6 in the OBD-connector, but there is no flashing of codes (should ABS-related codes flash here as well?..).

I have had the battery negative terminal disconnected for a few minutes -> the ABS-light is on as soon as I connect it again and start the car.

I installed a coilover-kit on the car, which made it substantially lower than stock. But this should not be related, I suppose.

I suppose the problem have nothing to do with the rear wheel speed sensor, since the speedometer is working as normal.

Anyone have any ideas? Thanks in advance!

[bkorven]

(accidentally quoted myself when I was about to modify my original message, hence the reply)

[Doctor Gollum]

You suppose incorrectly on several points.

The sensors themselves are correct. The Speedo is driven by the ABS ECU, and whilst it is rumoured to use the front left sensor, speedometer issues point to a failed ECU rather than sensors. You need a proper Tech 2 to access the abs. Unless you can guarantee to spin the hubs evenly and consistently then you won't get a steady ready.

Fitting coil overs to an Omega is a waste of time,money and effort unless your aim is to make it undriveable.

As an aside, have you changed the wheels as part of this work?

[bkorven]

You suppose incorrectly on several points.

The sensors themselves are correct. The Speedo is driven by the ABS ECU, and whilst it is rumoured to use the front left sensor, speedometer issues point to a failed ECU rather than sensors. You need a proper Tech 2 to access the abs. Unless you can guarantee to spin the hubs evenly and consistently then you won't get a steady ready.

Fitting coil overs to an Omega is a waste of time,money and effort unless your aim is to make it undriveable.

As an aside, have you changed the wheels as part of this work?

Thanks for the response.

I see, I might get myself a Tech2.

No, I have not changed the wheels as part of this work.

[cam.in.head]

IF  everything was ok regarding the abs before you changed the front sensors then it suggests an issue with the actual new sensors or the fitment of them.
are you 100% sure the connections are good.
are you 100% sure the new sensors are fully fitted into their recess and that no debris remains in the hole that could affect the reading in any way.
was the car switched on with the old damaged sensors in place ? could this have shorted / damaged the abs ecu ?
the abs light should come on initially and then go off whilst you are not moving proving the system thinks all is ok and then if it comes on once moving means it has detected an abnormality .

[bkorven]

IF  everything was ok regarding the abs before you changed the front sensors then it suggests an issue with the actual new sensors or the fitment of them.
are you 100% sure the connections are good.
are you 100% sure the new sensors are fully fitted into their recess and that no debris remains in the hole that could affect the reading in any way.
was the car switched on with the old damaged sensors in place ? could this have shorted / damaged the abs ecu ?
the abs light should come on initially and then go off whilst you are not moving proving the system thinks all is ok and then if it comes on once moving means it has detected an abnormality .

I agree that it should reasonably be linked to the installation of the new sensors. Although I have found it strange that the light is on constantly, regardless of if the car is moving or not. And now you're confirming that it should not be that way, if it were only the sensors that give bad signals. That's good to know for certain, thanks.

Q: Am I 100% the connections are good?
A: No, but 99% sure. I haven't done much other than replace the sensors.

Q: Am I 100% sure the new sensors are fully fitted into their recess?
A: I have looked in between brake shield and the hub, and the gap seems to be very small. The distance is hard to measure, so I can't say for sure. I was hoping to be able to find this out by measuring the voltage while spinning the wheels.

Q: Is there any debris remaining in the hole that could affect the reading in any way?
A: Could be, yes. In order to fit the new sensors I had to sand the surfaces of the holes a little. I have cleaned the hubs carefully afterwards, but I guess I can't be 100% sure. Either way, this wouldn't explain the light being constantly on, would it?

Q: Was the car switched on with the old damaged sensors in place?
A: No, it was not. Would it be enough to only have the ignition on, to possibly have problems?

I am starting to believe the fault is somewhere else (perhaps with the ABS-ECU). I will see if I can get the error codes.

Thanks alot for your reply!

[cam.in.head]

to my understanding and assuming the ecu hasnt been damaged in any way the fact that the light comes on and stays on even before you  are moving suggests that the ecu thinks there is a problem.i would double check the connections and even recheck the resistance readings .if you can read the circuit diag it might be worth reading the resistances at the abs ecu plug itself.
i dont have any front ones to hand to compare but my spare rear ones measure 1.5 k ohms.

[LC0112G]

i dont have any front ones to hand to compare but my spare rear ones measure 1.5 k ohms.

...and measure the resistance to ground/shell/0V. This should be near infinite. A short between either terminal or the coil itself and the casing will cause the fault.

[bkorven]

I managed to fix the problem, and thought I would update the thread in case it can help someone else in the future.

In short, the problem was caused by:

[bkorven]

I managed to fix the problem, and thought I would update the thread in case it can help someone else in the future.

In short, the problem was caused by:

I somehow accidentally left the page with the just started reply, which I can no longer modify.

I managed to fix the problem, and thought I would update the thread in case it can help someone else in the future.

In short, the problem was caused by:
 - Dirt and metal debris on the sensor(s)
 - Incorrect sensor fitment (gap to reluctor ring too large, likely due to rust)

The active fault codes were:
 - C0035-8 Front Left Wheel Sensor incorrect signal
 - C0040-8 Front Right Wheel Sensor incorrect signal
 - C0245-1 Wheel Sensor Signal Circuit out of nominal range/performance


Rotating the wheel at about 2 RPM, initially, the signal from one of the sensors would look like this (noisy and weak):


After cleaning the sensor:


And after filing the hub, this is the best I could achieve:


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!

[Doctor Gollum]

You may find that the hubs require replacing as the reluctor ring on the fronts is part of the bearing assembly.

The magnet on the sensor will have field around it which is disturbed by the rotation of the hub. Moving the sensor away from its factory orientation may result in adverse abs performance.

[VXL V6]

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. 

[cam.in.head]

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 !

[bkorven]

You may find that the hubs require replacing as the reluctor ring on the fronts is part of the bearing assembly.

The magnet on the sensor will have field around it which is disturbed by the rotation of the hub. Moving the sensor away from its factory orientation may result in adverse abs performance.

I think you are right. I have noticed that the ABS sometimes activates when it should not. I tried returning the sensors to the original position, and the ABS light comes back on.

So next step will be to install new hubs with reluctor rings.

[bkorven]

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!