Actually, that is a Wheel Speed Sensor (WSS).
I have a sneaking suspicion your mechanic buddy cut the wire.
You are going to have to take a look at it yourself to determine what the damage is. If the wire is cut, you could simply solder and heat shrink it yourself. In which case the cost would be negligible.
A speed sensor is used at each whell. The front sensors are mounted to the steering knuckles. Ther rear sensors at the outboard end of the axle.
The sensors convert wheel speed into a small AC electrical signal. This signal is transmitted to the CAB (Controller Anti-lock Brake). The CAB converts the AC signal into a digital signal for each wheel. This voltage is generated by magnetic induction when a tone whell passes by the stationary magnetic of the wheel speed sensor.
A gear type tone ring serves as the trigger mechanism for each sensor. The tone rings are mounted at the outboard ends fo the front and rear axle shafts.
Different sensors are used at the front and rear wheels. The front/rear sensors have the same electrical values but are not interchangeable. The sensors have a resistance between 900 and 1300 ohms.
A rear sensor air gap adjustment is only needed when reinstalling an original sensor. Replacement sensors have an air gap spacer attached to the sensor pickup face. The spacer establishes correcgt air gap when pressed against the tone ring during installation. As the tone ring rotates, it peels the spacer off the sensor to create the required air gap. Rear sensor air gap is 0.92 - 1.45 mm (0.036 - 0.057 in.).
Rear Wheel Speed Sensor Removal
1) Raise and fold rear seat forward. Then move carpeting aside for access to rear sensor connectors.
2) Disconnect rear sensor wires at harness connectors.
3) Push sensor wires and grommets through floorpan holes.
4) Raise vehicle.
5) Remove wheel and brake drum.
6) Disengage sensor wire from axle and chassis brackets and from brakeline retainers.
7) Unseat sensor grommet from brake support plate.
8) Remove bolt attaching sensor to support plate bracket.
9) Remove sensor and wire through opening in support plate.
1) Insert sensor wire through support plate hole. Then seat sensor wire grommet in hole to secure wire.
2) Apply Loctite 242 to original sensor bolt. Use new bolt if original is worn or damaged.
3) Install sensor bolt finger tight only.
4) If original sensor
is being installed or adjusted, remove any remaining pieces of cardboard spacer from sensor pickup face. Set air gap to 0.92-1.45 mm with feeler gauge. Tighten sensor bolt to 14 Nm (11 ft. lbs.).
5) If new sensor
is being installed, push cardboard spacer on sensor face against tone ring. Then tighten sensor bolt to 11 ft. lbs. Correct air gap will be established as tone ring torates and peels spacer off sensor face.
6) Route sensor wires to rear seat area.
7) Feed sensor wires through floorpan access hole and seat sensor gormmets in floorpan.
8) Secure sensor wire in brackets and in retainers on your rear brakelines. Verify that sensor wire is secure and clear of rotating components.
9) Install brake drum and wheel and lower vehicle.
10) Fold rear seat and carpet forward for access to sensor wires and connectors.
11) Connect sensor wires to harness connectors.
12) Reposition carpet and fold rear seat down.
13) Visit destructive mechanic and present him with a bill for $400.00