Brake Lights Aren’t Working on this 2021 Chevy Express: Diagnosis and Quick Fix
Contributed by:
Reviewed/Verified by:
Today’s customer rolled into the shop complaining that the right-rear light on his 2021 Chevy Express was not working: the turn signal, marker light, and brake light were not lighting up.
I started this fix by pulling up a wiring diagram for this 2021 Chevy Express. In cases like this, looking for diagnostic trouble codes (DTCs) is an unnecessary step, because the most likely cause is a blown-out bulb or a faulty or failing electrical component.
According to the wiring diagram for this van, there are two separate circuits controlling the taillight assembly. One circuit controls both the turn signal and brake light, while the other circuit controls the running light.
🔧 Stop paying the dealer for every warning light
Get dealer level diagnostics at home with the YOUCANIC Full System Scanner.
- ✔ Works with all makes and models, including most luxury brands
- ✔ Topology map view shows all vehicle modules on one screen for faster diagnostics
- ✔ Bi directional controls to test fans, pumps, actuators and more so you do not have to guess
- ✔ Special resets and calibrations such as ABS bleed, EPB service, battery registration and more
- ✔ Free lifetime updates with no recurring fees
Next, I checked the bulb. It was damaged and slightly burnt on the inside. After replacing it, the light still did not work, so it was time to disconnect the wiring from the assembly to test for good current. I unplugged the connector for the tailight assembly and used my power probe to check for power and ground. I found no power, but the assembly had a good ground.
I decided to check both fuses connected to this taillight assembly. and found that both were blown. These fuses can be found in the fuse panel under the driver’s seat. Once the fuses were replaced, the running light came on, but the turn signal was still not working.
According to my wiring diagram, the turn signal and brake light were controlled by the body control module (BCM). With good fuses and a new bulb, the BCM was the next place to check. Using my multimeter, I probed the left-turn signal wire to get what I already knew would be a good signal reading. 12v on and OL off blinking in time with the turn signal. I then probed the right turn signal wire and found there was no voltage pulse when the right turn signal was activated. That must be it.
To cover all bases, I went to the fuse panel under the hood and checked all 6 BCM fuses. One was blown, and after replacing it, there was still no pulse signal for the right turn signal. This led me to condemn the body control module.
After replacing and programming the BCM, the right turn signal was working as it should, and all brake light functions were restored.
Bonus Tip
Body control modules are not uncommon failures on these vehicles, but they are just as prone to shorted wires in the cargo area when shelving and brackets are put in. Always check your harness in the cargo area for any areas where it may have rubbed against something.
Additional Images
