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ABS light on after hub replacement

Hi - 05 Mazda 3. I recently replaced the brake pads, rotors and hub assemblies on both rear wheels. I was able to remove the ABS sensor off the old hub and re-connect it to the new hubs without incident. Put everything back on and brakes work fine, but the ABS light is on on the dashboard. Took it to a parts store thinking the code just needed to be reset but they tell me that it doesn’t read that there are any errors, although the light stays on. I don’t see the point in removing anything (I did reach under and checked the abs connector and it seems just fine), but is there any reason for this light to be on? Anything I can check that might cause it? Thanks in advance.

Here’s a link to how to test an abs sensor. Give it a try.

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Was the light on before? Did the Tone Ring get damaged when you played with the Hub?

According to my AllData it looks like that bearing has the encoder built in and the encoder section must be installed to the inside of the car. So maybe you put it in backwards??


In my opinion, the tool the parts store was using is incapable of properly retrieving abs fault codes on your vehicle

Not all cheapo code readers . . . the kind that the parts store most likely has behind the counter . . . are even capable of retrieving abs fault codes

That said, I think it’s quite possible the counter guy grabbed one of those, hooked it up and didn’t retrieve any codes . . . not realizing the tool only retrieves engine control module codes

Most likely, the abs light remains on because of an issue with the rear speed sensor(s)

I advise you to read thevlink that mountainbike sent you

OK. Thanks. No problems before with the light. It’s just on, not flashing, blinking or doing anything else. I removed the ABS plug from the old hub before removing the old hub, then after the old hub was removed, i removed the ABS sensor from the hub and put it on the new hub – the new hub didn’t have the sensor built in, just the area to plug it into. The shop manual and everything I found online didn’t mention anything about the encoder location. I’ll check that today. The plug was kind of an oval shape, so I’m assuming the encoder is (according to your picture) the smaller oval. I should be able to verify that before taking it all apart again – which wasn’t exactly fun.

Thanks for the ideas.

Sulldrinker - are you saying the hub is backwards, or the sensor plug? I looked at the old hubs, and the new ones I put in, and the bolt pattern is not a square. They look like there is only one way the hub can go in, and only one way the sensor can go in also. My jack went on the fritz, so I’m in the process of getting a new one - I just want to know what I’m looking for. And if you are talking about the hub itself needing to come off and be rotated 180 degrees, how do I tell which hub is “backwards”, and I read someplace that said the magnet can somehow mean you have to replace the hub again – which to me seems ludicrous. Is an alternative to disable the ABS, since this activates maybe 2 times a year in my climate.

If the ABS light was not on before you replaced the sensors and now it is then it probably has something to do with a part/parts or your installation of them (Which, as you pointed out is pretty straight-forward, hard to screw up.).

As @db4690 said, “Not all cheapo code readers . . . the kind that the parts store most likely has behind the counter . . . are even capable of retrieving abs fault codes”

ABS and SRS (air bag restraints) use unique codes, B & C codes, not the P codes picked up when a “Check Engine Light” illuminates.

You can test as outlined by the link posted by @the_same_mountainbik or get somebody to read the codes that has that capability.

Otherwise, you are grasping at straws.

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Are you sure that the new hubs even have a tone ring.

I’ve ordered hubs and many times their was a choice of with or without ABS.


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Yes. I ordered the hubs “with ABS”. Im going to try and attach a photo of
the old hub. The new one looked exactly the same. I removed the ABS sensor
off the old hub with a 5mm and put it on the new hub. I dont know anything
about a tone ring, this hub is completely sealed.

The “tone ring” is a series of alternating-poled permanent magnets circumferentially placed around a rotating part of the hub, which might not be apparent just by looking at it. But if you place a piece of steel, like the tip of a screwdriver, next to the tone ring where those magnets are located you should be able to feel a slight magnetic pull. Try that experiment on the old hub.

It’s worth checking the connector to make sure a pin didn’t get bent or it’s properly seated etc. It’s about the only thing that could go wrong in the replacement process.

Was the indicator illuminated immediately after you started the engine but before you drove it?

Thanks, TwinTurbo — I’m going to check that next. I don’t remember if it
was illuminated right after or not — I seem to think it wasn’t, then came
on. My next step is to do the OHM testing mentioned earlier in this thread
to try and isolate it. I think there might have been some confusion earlier
as to the repairs I did (maybe not) - but to clarify for anyone else having
similar issues, I replaced not just the hub bearings, but the entire hub
assembly (see pic posted earlier). So I’m thinking those issues with
backwards, etc. are not applicable. Thanks for all the suggestions.

It’s possible you inadvertently damaged the sensor in moving it to the replacement hub. They have coils of very tiny wires inside, and even a slight bending force on the part might break one of the wires. Especially one that has been in use for many years. I had a similar problem with a lawnmower magneto which works on the same principle. It was working fine until I removed it to make room to work on something else. Didn’t work after it was re-installed, ohm test showed the coil wires had broken.

Sorry but I said Tone Ring before I looked up your car and see that there is no tone ring on your hub or on the axle.

sorry again I read too fast and thouhgt you were working in the front wheels. Yeah the rears you couldn’t have mess up they simply bolt it.

Your tone ring is built in.

Thanks, Skulldrinker. Yes, I ran a screwdriver across the old hub and the
entire hub ring is magnetized (across the 4 mounting bolt pattern. Since I
replaced the sealed hub, I don’t think it’s anything to do with that – it
can only go in one way. What makes more sense is that when I removed the
clip, it somehow damaged the pin. I haven’t had a chance yet, but I’m
intending to test the ohms of the connectors and try and isolate the issue.
My guess is that the connectors need to either be cleaned or replaced, or
possibly the sensor itself. At any rate, none of these parts are
particularly expensive. I will post back the results once I figure it out.

And FYI - I did NOT press the bearing out. Since the cost to replace the
entire hub (at least for me since I’d have to pay to have someone press it
for me) wasn’t much more than the bearing itself (like $20), I replaced the
entire hub.

OK - I wanted to post the resolution to this issue for others. I pulled everything off and tested all the sensors and wires with a multimeter. They all tested the same (3,000 I think). Gave up and took it to a shop. They verified that one of the hubs I had purchased online, even though it was labelled as “with ABS” and had the hole where I screwed the old ABS sensor into, did not have the sensor ring inside the hub. New hub with the ring, and ABS light went away. Since I’m a novice, I would have never figured that one out – and I’m not sure how I could have tested the new hubs before installing them.Thanks to everyone on the forum for their help!

Thanks for the follow-up post OP, good for you for sticking with it and getting that pesky ABS light to turn off. I would have guessed it would be possible to sense the alternating magnet effect of the tone ring with the tip of the screwdriver, comparing one with a tone ring vs one without would show you one of them was missing the tone ring. But apparently the effect is too slight to sense that way. Maybe a magnetic needle compass gadget would have worked. I use one of those to test for the magnetic poles in electric motors sometimes. You said the entire hub seemed to be magnetized, and that overall magnetization might masked any tone ring effect. Curious, I wonder why the entire hub was magnetized? Maybe you’ve discovered something there OP, some kind of new fundamental physics of rotating steel? … lol …

At least the vehicle is finally fixed

I hope you’ll try to get a refund from the online parts store. That was a rather silly mistake on their part

Yes - the online parts store did offer a refund and free return shipping.
But to be honest ill likely pay a little more in the future and buy local.

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