No brake lights, dahs bord, inside, fuses look good

there are two filaments inside each bulb for tail lights ,one does running lights and one does stop lights

try replacing bulb it's the least expensive method

sounds like one of two things, your bulbs are burnt out or your brake light switch is no good, the switch has 2 parts inside of it, one for ther brake lights and one for the 3rd brake light

WITH A GOOD FUSE TESTER, TEST ALL THE FUSES FUSEBOX UNDER THE HOOD & INSIDE THE VEHICLE. IF THE FUSES ARE ALL GOOD WITH THE TESTER YOU MUST HAVE A BAD BRAKE LIGHT SWITCH OR A BAD TURN SIGNAL SWITCH. THE BRAKE LIGHT CIRCUIT GOES UP THROUGH THE TURN SIGNAL SWITCH & THEN TO THE BRAKE LIGHTS. FIRST OF ALL IS THE BRAKE LIGHT SWITCH GOOD ? THE ORANGE WIRE FEEDS THE BRAKE LIGHT SWITCH, THE WHITE WIRE PUTS POWER TO THE TURN SIGNAL SWITCH, SO THE LIGHTS CAN BE USED AS TURN LIGHTS OR BRAKE LIGHTS. , PUT A TESTER IN THE WHITE WIRE & PRESS ON THE BRAKE PEDAL. IF THE TEST LIGHT LIGHTS UP, BRAKE LIGHT SWITCH IS GOOD, BY THE WAY THE BRAKE LIGHT FUSE MAY BE LABELED" STOP", THE FUSE LABELED" BRAKE" IS FOR THE ABS SYSTEM. TO CHECK THE TURN SIGNAL SWITCH FOR BRAKE LIGHTS, REMOVE THE PLASTIC COVER FROM UNDER THE STEERING WHEEL, PRESS ON THE BRAKE PEDAL, PUT THE TESTER IN THE SMALL YELLOW WIRE, THEN THE SMALL GREEN WIRE. IF THERE IS NO POWER IN EITHER WIRE, THE TURN SIGNAL SWITCH IS BAD.

THE FUSE FOR THE BRAKE LIGHTS MAY BE LABELED " STOP ". GM USES BRAKE FUSE FOR THE " ABS " HOWEVER, THE FUSES NEED TO BE TESTED WITH A FUSE / CIRCUIT TESTER, IN THE FUSES BOX UNDER THE HOOD & THE FUSE BOX INSIDE THE VEHICLE.

CHECK BRAKE LIGHTS FUSE IF FUSE GOOD CHECK FOR POWER AT BRAKE SWITCH.IF YES BRAKE SWITCH FAULTY.IF NO POWER TO BRAKE SWITCH YOU HAVE A OPEN WIRE FROM THE BRAKE LIGHT FUSE TO THE BRAKE LIGHT SWITCH.

If the two rear brake light are working on each side, then fuse and relay are good, check the bulb.

I'm not sure about the location of a particular fuse, but it is good practice to check all of the fuses anyway. Once you have checked all of the fuses that are inside, there is a separate set under the hood. There should be a diagram on the inside of the cover. After checking all fuses, there are relays associated with the brake lights. They are located in the same box under the hood. You can not check it, you will have to replace it. Have you replaced the bulbs? If the problem is your brake lights, it might be the switch that is associated with your brake pedal, which activates the lights. If it is the running lights, then it is most likely a fuse or relay. The running lights are the ones that come on when you turn your headlights on.

sounds like one of the circuit bords at taillights is bad

I would definitely go after the brake light switch under the L/S dah at the brake pedal . Sounds like it might be sticking. Hope this helps

From what you just said i dont belive the mechanic checked your fuses correctly.

Check your self to confirm, But if no avial i belive the controller for your lighting may be fried.