1994 940 sedan, non-turbo with 311k miles. No prior work done to the ABS module that I am aware of. I've owned the car since 2002. Recent brake work, I replaced the master cylinder a few weeks ago. Brakes are fine, pedal operates normally, and no warning lights illuminated in the dash.

Replaced the master cylinder because brakes smelled hot at all four wheels after my wife came home from a 10-15 mile drive. After replacing the cylinder, brakes were fine and hot smell went away.

Now, the right front brake smells hot after my wife drove the car for 10 miles. Thinking the caliper might be stuck, I jacked up the front to feel for any resistance against turning the wheel. But when I spun the wheel, there was a hissing noise coming from the ABS module. The noise continued for a second or two after the wheel stopped turning. It sounds like maybe the module motor is running.

Same noise when the left front wheel is turned, but no hot brake smell from that side. No symptoms when spinning the rear wheels and no hot smell from the rear either. There was no unusual or unexpected resistance against spinning any of the wheels by hand, in fact they all seemed to spin as expected.

Now I wonder if there is something wrong with the ABS sensor for the right front wheel or if the ABS module is going bad. I'm guessing the ABS is engaging the caliper even while the brake pedal is not pressed.

Anyone with experience on this that can point me in the right direction?
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1994 944 310,000 miles and rolling