While pressing brake pedal then turn signal doesn't work in the rear of the vehicle and the brake lights are not bright like they should be? On the dash it show as if the four ways are on..any sug

Kevin , this is a very complex way of stoplamp control , I will post GM service Description and Operation of how they work an let you deside if you want to tackle this ! Do the center high mount brake lights work ?
The brake pedal position sensor is a resistive device used to sense the action of the driver's application of the brake pedal. The brake pedal position sensor provides an analog signal that will increase as the brake pedal is pressed.
The brake pedal position sensor receives both a 5-volt reference voltage and a low reference signal from the electronic brake control module (EBCM). When the brake pedal is pressed, a variable signal is applied from the brake pedal position sensor to the EBCM through the brake sensor signal circuit. The fuse block left rear supplies battery positive voltage to the bass relay switch through the BASS fuse. One side of the bass relay coil is permanently grounded at G402. The EBCM supplies voltage to the bass relay coil upon receiving the signal from the brake pedal position sensor. The switch contacts of the bas relay close and battery positive voltage is applied through the bas relay switch to the center high mounted stop lamp (CHMSL), and to the turn signal/hazard flasher module through the stop lamp switch signal circuit. The ground for the CHMSL is applied from G402. The turn signal/hazard flasher module then supplies voltage to the left and right stop lamps in the tail lamp assemblies that have ground at G401 and G402. For export vehicles the stop lamps receive battery positive voltage directly from the bass relay.

There could be a code stored in the EBCM - electronic brake control module - DTC B3903 Stop Lamp Relay Circuit
DTC C0278 Brake Pedal Position Sensor Not Calibrated
there are several other codes that pertane to the brake lights . you could try Replaceing the bas relay !
Fuse Block - Left Rear
In the passenger compartment, under the left side of the rear seat at carpet.

Check for loose contacts or wiring that is causing a short circuit near the brake pedal, or at the rear light.

bad earth the wire that goes to the car body could be lose

I can almost 100% guaranty the turn signal switch is the problem. Power for the brake lights starts at the brake switch. power then splits from there and the third brake light gets power directly from the brake switch. Since the turn signal and the brake lights are on the same bulb power for the brake lights is routed through the turn signal switch. the switch depending on what position it is in will allow brake power or turn signal power to there respective left or right brake/turn bulbs.

If you hold your foot on the brake pedal and wiggle the turn signal and or play with the hazard switch the brake lights will almost always intermittently start to work. this will confirm a bad turn signal switch which is pretty common on GM vehicle with this style setup.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

Most likely this is a brake light switch issue. Replace switch.

If your emergency flashers don't work, all flasher bulbs are fine, but flashing too fast, then check and replace Hazard light switch.

Sounds like a faulty signal switch.Here's a way to check it,hold the brake pedal down while pushing down on and wiggling the hazard switch.If the brake lights come then replace the signal switch.

If your rear brake lights are on all the time, I would first check your brake pedal. Near the top of the pedal, probably just about where the pedal is attached to its pivot, you'll see a little switch that is either pressed in or released when you step on the brakes. That's the switch that controls your rear brake lights. As an experiment, have a helper look at the brake lights while you manually pull or push this switch all the way in and out. These switches wear over time and can stick in position. Fortunately, they're not expensive to replace, if that turns out to be the problem.


If your brake light switch seems to be working properly (hard to tell if the brake lights won't go off), a second possibility is that there's a short somewhere in your wiring and your brake lights are getting power from the shorted wire. I think this is a pretty unlikely cause, because most of the wires that rub up against the brake light wiring are for your turn signals and tail lights, and these are not normally energized. If you said that your brake lights always came on when you activated your turn signal or when you turned on your other lights, then this cause would be much more likely.


Check your brake pedal switch and the wire connections to it. I have a feeling that you'll find your problem.

The first step is to check the bulbs in the tail lights. The brake light switch (on the brake pedal) is OK, as the center light works.

If your rear brake lights are on all the time, I would first check your brake pedal. Near the top of the pedal, probably just about where the pedal is attached to its pivot, you'll see a little switch that is either pressed in or released when you step on the brakes. That's the switch that controls your rear brake lights. As an experiment, have a helper look at the brake lights while you manually pull or push this switch all the way in and out. These switches wear over time and can stick in position. Fortunately, they're not expensive to replace, if that turns out to be the problem.

If your brake light switch seems to be working properly (hard to tell if the brake lights won't go off), a second possibility is that there's a short somewhere in your wiring and your brake lights are getting power from the shorted wire. I think this is a pretty unlikely cause, because most of the wires that rub up against the brake light wiring are for your turn signals and tail lights, and these are not normally energized. If you said that your brake lights always came on when you activated your turn signal or when you turned on your other lights, then this cause would be much more likely.

Check your brake pedal switch and the wire connections to it. I have a feeling that you'll find your problem.

Replace the turn signal switch. All of these lights run threw it.