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(Car #1 - 2012 Impreza) In the past I've changed both front bearing/hub assemblies on one of my Subarus, and that went fine.

(Car #2 - 2011 Forester) Now I'm working on our other car - different model Subaru but its all exactly the same procedure & parts for the front hub as the first one I did.

So I swapped in the new hub/bearing without any mechanical issues. Then took the car for a 1 mile test drive and that was also fine (no dashboard lights). Thought I was done.

The next day we take #2 out and immediately all the dash lights come on when its started - ABS, traction control, check engine, a few others. But nothing sounds odd and I drove it about 100 feet, it operated fine.

Reading around the subject it sounded like this could be an incompatibility between the hub & the ABS sensor... and I did happen to use a different brand of hub on car #2 than I did on #1.

So today I replaced it with a new one using the known-good brand. But its exactly the same problem.

At this point I'm looking for advice on how to diagnose this. I guess there are at least two possibilities:

  1. ABS sensor is broken.
  2. Both hub assemblies are defective.

I would have thought #1 in the first place, except that it did work for that very first test drive. I thought this would have eliminated the sensor from being a possibility?

Is there any way to test the sensor itself? If I pull it out is it likely I would noticed a problem visually?

Misc.

I've left the sensors in place when I've done these hubs and was very careful with them. I had read that sometimes trying to remove them can result in a broken bolt (here in the rust belt) and that seemed like it would be a much worse problem. But that might have left it subject to damage.

The hub assembly includes the ring that the sensor reads.

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    Have you checked your battery voltage? I realize this has nothing to do with wheel sensor and I believe your issue may be unrelated to the work you've done (ie: coincidence). Your description makes me believe one of two things: (1) you've got a grounding issue somewhere; (2) the battery has enough charge to start the engine and run it, but not enough to run the electronics. This "spot" where it can happen is somewhere in the 10.50-11vdc range. If the battery is going bad, it could be the issue.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Dec 26, 2021 at 20:45
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    Tried AutoZone for a free reading of abs error codes? Call ahead to be sure they have a reader capable of decoding abs errors. There's at least one YouTube video on measuring abs wheel speed sensor resistance. Damaged wiring to each sensor is a possibly too.
    – F Dryer
    Dec 26, 2021 at 20:47
  • @Pᴀᴜʟsᴛᴇʀ2 a battery problem would be too good to be true, but that doesn't mean it isn't :) Key OFF battery reads a little under 12 V, Key ON (but engine not running) it was around 9-10 V. So I have it on a charger for a while and we'll see what happens. This is definitely worth checking at least because its so easy.
    – StayOnTarget
    Dec 27, 2021 at 16:19
  • I had a ABS sensor bolt break just last week. Which model Subaru is car #2, can you list the codes? I guess you didn't damage the sensor wire harness is there any dirt or debris around the ABS sensor or holes.
    – ajayel
    Dec 27, 2021 at 20:26
  • @ajayel #2 is a Forester. I don't have a way to list out the codes... The sensor itself seemed clean; I did wipe down the bearing insert hole and blew it out with air before installing the new hub. I don't think I damaged the wiring in any way.
    – StayOnTarget
    Dec 28, 2021 at 14:21

1 Answer 1

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This is what ultimately resolved the problem in total, but it wasn't 100% clear how these things were related.

  1. I got an OBDII reader and it did show a code for bad wheel speed sensor. So I replaced the sensor. (At this point the car would electrically power on normally).

  2. After that, the car would not even start. Turned out the battery was dead flat. After some investigation found that the (+) terminal was basically disintegrating. Charged the battery with an external charger, replaced the terminal, now the car runs perfectly.

In a comment @Pᴀᴜʟsᴛᴇʀ2 had suggested that a battery problem could cause a false indication of a bad sensor and/or the other phantom problems shown in the dashboard. Given that indeed there was a battery issue, this makes me question whether the sensor was really bad. Had I discovered the battery problem earlier I would certainly have fixed that first.

I haven't yet tried to test the old sensor itself, I may do that just out of interest. But otherwise I don't think what happened here will ever be crystal clear. Its possible there were just two independent problems, failures unrelated except by the age of the car and its OEM parts.

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