Sounds like you've got two different problems, because the brake lights and turn signals are on different circuits.
1. Brake lights. These should work whether the engine is on or off. Check fuse box for a blown fuse. If OK, check for voltage at one of the lights with the brake pedal depressed. If no voltage, brake light switch under dash probably bad. Fairly easy replacement.
2. Flashers/turn signals. The flashers should work with the engine on or off. If they don't, might be a bad fuse. If that doesn't fix it, might be a problem with the wiring connected to the turn signal switch, or the switch itself.
Actually thats not true the chevy uplanders did not have seperate turn signals and brake lights in the back it was a combined brake turn signal sent from the bcm (body control module)
Why are you commenting to a post that was posted in 2018
Why comment 2 years later like “Anthony DeVor” did on the original post and like I am doing on your post? Perhaps because the forum is intended to help people and while his 2-year-old post won’t help the original poster it is useful to people like me who are currently experiencing this issue and for people who may come across this problem in the future.
Big deal , probably not the same issue. never is with vehicles that old. Rust buckets with bad grounds, corrosion in the sockets. Shorted out wiring ,bad BCM.
Not telling how much you people messed with your vehicles , thinking you know how to repair your vehicles.
Most of you people end up taking it to the dealer or some other repair shop in the end . You look for a common fault that isn't there. You have no clue how these thing's work. The BCM controls the turn signals an hazards. Hooking up a scan tool an checking for codes in the BCM would be the first place to start . So don't get on your high horse . Do you know how to test electrical circuits ,computer controlled circuits ?
Turn Signal Lamps
The STOP/TURN fuse in the instrument panel (I/P) fuse block supplies battery positive voltage to the body control module (BCM) for the turn signal lamps. When the turn switch is placed in the left or right position, ground is applied to the BCM on the left or right turn signal switch signal circuit. The BCM then applies voltage to the appropriate front and rear supply voltage circuits.
Grounds for the various lamps are as follows:
• G100 supplies the right front lamps
• G101 supplies the left front lamps
• G400 supplies the right rear lamps
• G401 supplies the left rear lamps
Get out a voltmeter an do some voltage drop testing , do you know what that is ?
B3445: Stop Lamp Circuit
Circuit/System Description
The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The body control module (BCM) provides a low reference signal and a 5-volt reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery voltage to the right and left stop lamp control circuits, transmission control module (TCM), electronic brake control module (EBCM), engine control module (ECM), and center high mounted stop lamp (CHMSL) control circuit.
DTC B3948: Left Front Turn Signal Circuit
Circuit/System Description
Ground is applied at all times at G200 to the turn signal/multifunction switch. The turn signal lamps may only be activated with the ignition switch in the ON or START position. When the turn signal/multifunction switch is placed in either the TURN RIGHT or TURN LEFT position, ground is applied to the body control module (BCM) through either the right turn or left turn signal switch signal circuit. The BCM then applies a pulsating voltage to the front and rear turn signal lamps through there respective voltage supply circuits. When a turn signal request is received by the BCM, a serial data message is sent to the instrument panel cluster (IPC) requesting the respective turn signal indicator be pulsed ON and OFF.
DTC B3949: Right Front Turn Signal Circuit
DTC B3950: Left Rear Turn Signal Circuit
DTC B3951: Right Rear Turn Signal Circuit
DTC C0277: Brake Pedal Position Sensor Circuit
DTC C0278: Brake Pedal Position Sensor Not Calibrated
DTC C0283: Brake Pedal Position Sensor Circuit Low
Circuit/System Description
The hazard flashers may be activated in any power mode. The hazard switch is located on the multifunction switch-I/P and is permanently grounded at ground G200. When the hazard switch is placed in the ON position, ground is applied through the hazard switch signal circuit to the body control module (BCM). The BCM supplies battery voltage to all four turn signal lamps in an ON and OFF duty cycle. When the hazard switch is activated, the BCM sends a serial data message to the instrument panel cluster (IPC) requesting both turn signal indicators to be cycled ON and OFF.
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SOURCE: 99 Chevy Tahoe... Rear turn signals, brake lights, and hazards
I had this problem, and to be honest, it happened to the left side about a week later...it's the board that the bulbs plug into...it's a very common problem with this model. So popular that you can normally get the socket board off the shelf at a parts store! it's extremely simple to replace, and I replaced all the bulbs at the same time!
SOURCE: 1992 Ford Ranger Turn signal/Hazard light issue
Can you just check to make sure the ignition key switch is not staying over to far and not backing off when you try to start it. I had a truck that did that and it messed up my turn signals until I brought the key switch back a little after starting it. Just a simple idea. Be kind with your rating for me. Raz
SOURCE: my 97 chevy blazer, the brake lights dont work but
More likely it is the hazard/turnsignal/highbeam/cruise control switch module. It costs about $275 for the module. However there is a repair kit for the likely culprit...the hazard button. Try jiggling it around a little, see if that helps. Spray a little WD-40 into it so it can jostle back into it's correct position. You could try a junkyard unit or Ebay. It's not too hard to change. The hard part is doing it without removing the steering wheel. It can be done. I've done it. But hopefully you can locate the repair kit which costs about 15 dollars. Good luck.
SOURCE: jaguar xj6 break light cancels signal
Replace the turn signal switch. Bad contact inside causing a crossing of the circuits. When the turn signal is applied it should open the brake light circuit allowing for just the signal to work. Doesn't sound like the switch is doing it's job.
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