First thing to do is change the brake fluid in master cylinder and then bleed all four corners, taking special car with the rear brakes...takes a lot of fluid to go through that abs system which in your car is under the trunk cover in the right rear corner.

Next I would disconnect and clean and reconnect the three connectors for the sensors...the front two are wheel sensors and the rear one is in the diff. The connectors sometimes/often give problems.

Next I would pull the front discs (have to remove the front calipers, don't have to disconnect brake lines, just hang the calipers with a piece of coathanger wire...now would be a good time to check out the slider bushings and put in a rubber boot/slider kit if necessary. With the discs off you can see the sensor and tone wheel...if it's crudded up clean them carefully, no wire brush, just get the crap off. If it's a patently bad (mechanically broken or cable torn/broken, replace the sensor...comes with a new cable).

Put it all back together and if it still doesn't work take it to a dealer with the abs testing tools/equipment. A new front wheel sensor installed was about $180 two years ago...probably $250 today. OTOH, you might be able to replace both front wheel sensors yourself for that money, but they can be a b#%$#h to remove. Not to mention the tonewheel may be the problem which is why the test equipment is useful.