Reverse lights not working.

These lights are all computer controlled ! Several modules involved DIM - dash integrated module , RIM - rear integrated module .They share information on serial data communication network . Class 2 an or GMLAN !
The rear fuse block supplies battery positive voltage through the REVERSE LAMP fuse to the coil and switch terminals of the reverse lamp relay. The DIM sends a power mode message to the RIM indicating that the ignition is in the ON position. When the driver of an automatic transmission equipped vehicle places the gear selector in the REVERSE position, the powertrain control module (PCM) sends a class 2 message to the RIM. The message indicates that the gear selector lever is in the REVERSE position. When the driver places a manual transmission equipped vehicle in reverse the reverse gear position switch mounted on the transmission closes. This provides a ground for the reverse gear position switch signal line, informing the RIM that the transmission is in reverse. For both automatic and manual transmission vehicles the RIM then grounds the control circuit of the reverse lamp relay . This energizes the reverse lamp relay, closing the switch side contacts and providing battery positive voltage to the backup lamp bulbs. The backup lamps are permanently grounded at G402. With both power and ground the backup lamp bulbs illuminate. Once the driver moves the shift lever out of the reverse position a message is send either by class 2 by the PCM or the reverse gear position switch opens causing the RIM to remove the ground from the reverse lamp relay control circuit. This opens the contacts in the relay turning OFF the backup lamps.
This is something best left to the dealer or a ASE certified repair shop . Need a factory or professional grade scan tool to diagnose an repair this . http://www.public.asu.edu/~pheanis/documents/VBI_CAN.pdf

Reverse switch bad located in the gear selector

If bulbs are good then you need to check the switch that powers them when you put the car into reverse.

FYI - Neutral safety switch prevents car from starting unless it is in neutral transmission position only.

Does you shift indicator point to "R" when in reverse. The reverse light are switched on by the selector shaft position sensor built into the Parp/Neutral Safety Switch. It may be bad or just out of adjustment.

switch ignition on but do not start engine, select reverse gear and then you can get out and have a look if it is working

Follow these steps:-
- first check both bulbs.
- Next check you got voltage/Ground on the bulb holders.
- Bulb holder contacts may be bad if you get voltage.
- If no Voltage on Bulbs when Gear shift is at 'R'.
- Check Fuse, broken wires, check the switch under gear shift
which closes circuit when G/Shift is at 'R' position.

I’m happy to assist further over the phone at https://www.6ya.com/expert/uttamjeet_2f3adc18600f8ede

Check for voltage at the neutral safety switch if the bulbs are good.
The switch also powers the backup light bulbs in reverse.

You checked fuse # F24 in the central junction box. Do you have a volt meter ? check for B+ voltage at the switch ,in an out pushing on the pedal . The orange with yellow stripe wire is power out of the switch .Check out the wiring diagram at http://www.bbbind.com/free_tsb.html do you know how to read a wiring diagram ?

Have you checked for voltage at the light socket with the bulbs removed? If no voltage, then you may have a bad reverse switch. If you have voltage, (with car off, car in reverse, and ignition on) the try new bulbs. Even a bulb that LOOKS good can be bad

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/sean_54c3a3dc48a7773c

The switch is located on the side of the transmission. There is a 2-wire connection, (I believe they are coloured black/orange and red/white. If you unplug the connector and jump the 2 wires together the lights should go on. If they do then the switch is dead, if not there's something else wrong.