Can ABS cause slight drag on one wheel with no hint that it is doing so?

Hypothetically...

If an ABS sensor on one wheel was damaged just a tiny bit, for instance when a wheel bearing was replaced, is it possible that it might send a signal that was almost but not quite perfect to the ABS unit, and if so, might the ABS unit respond in such a way that the brake on that wheel was only very slightly applied? All of this going on silently, with no warning light or code?

I'm imagining this as the sensor sending a series of evenly spaced pulses and the damage causes just one (or a small number of adjacent ones) to be noisy and so instead of 1 or 2 rising edges per unit time there are many more, let's say 5. The ABS unit seeing 5 on that one wheel and 1 or 2 on all the others starts to do "wheel is slipping" and begins to squeeze the caliper there, but before it can really get going it is back to regular pulses for the rest of that rotation. Unclear why it wouldn't light up the indicator, unless perhaps it is doing so, but at a duty cycle of 1 in 100, making it too dim or brief to see. I'm thinking the ABS unit should throw some sort of code for this scenario though.

 

Yes, chasing a slight drag. After eliminating tires as the problem I finally took the car to a mechanic I trust for more difficult problems and he reproduced the issue but couldn't find anything that clearly accounted for it. The drag is slight enough that he couldn't even see the difference in brake pad wear between the two sides over 10k miles. Said he couldn't feel the difference in drag between the two sides and couldn't hear any sounds from the bearing. Not surprised he couldn't feel it - to heat the wheel by only 10 degrees F wouldn't require very much friction at all. Anyway, he said the lubrication on the brake components didn't look up to snuff, so he redid that, and we will see if that fixes it. Fingers crossed. Had him change the brake fluid while he was at it.

He did say that the ABS can sometimes cause strange problems like this. If the problem is ABS related I suspect that it would only kick in once the car is on (probably wasn't when he was spinning the wheels by hand) and might not show up until the wheels are spinning at a reasonable speed. Anyway, one possibility is that the shop which changed the bearing slightly munched the ABS ring on the wheel. I mean, there is a 25% chance at random, but odd that the wheel that has this problem is the one that had a bearing changed.

My impression was that if it was his car he would have waited until it got worse before trying to fix it. Problem is, with my luck that would happen 200 miles from anywhere on a vacation trip, so I prefer to fix problems early.

ABS history screen is in Techstream somewhere? How long are the events stored there?

 

After a 10 minute drive today the same wheel was again found to be 10 F hotter. (Hand test, didn't have a thermometer with me.) Rats.

The issue with rubber in the brake line isn't like this. What happens there is that the driver steps on the brake which pushes fluid into the piston, but when the foot comes off the brake the flap of rubber swings over and blocks movement of the fluid away from the piston, so it stays engaged. Pretty obvious when a brake is engaged when it shouldn't be. That is not what is happening here. At least it wasn't when we looked for it before. Put the front of the car up on jacks, turned it on, put it in neutral, spun the front wheels (base line resistance), stepped on the brake (they would not spin), released the brake, immediately spin the wheels (like the baseline, at least as far as we could tell).

On the plus side, 10 F more isn't going to damage anything mechanical, although I guess it will pull down the MPG slightly. I wonder how many watts it takes to heat a wheel 10 degrees? A wheel and the attached knuckle and rotor is a pretty huge heat sink and has cooling air blowing over it whenever the heat is being generated.

 

I will take a look at some point - when it is a little cooler out. If it shows 4 (which it should if this is happening all the time) then I'll unhook the 12V battery and see how long it takes for them to return. I don't think I have ever even looked at the brake data fields in Techstream. If it has ones for brake activation and ABS sensor data at each wheel that would be helpful.

 

Interesting idea. I do have a big beam torque wrench, have to think about how to do this without it smacking into the ground.