If I trip the sensor by driving the car outside, the light goes on. The remote won't work. If I then go in the garage and push the button to turn on the light and then leave the garage without tripping the sensor, the remote functions normally.
This is a Chamberlain Lift Master using a Clicker remote. The problem started recently after 15 years of faultless service. The EMF idea suggested in comments sounded great, but didn't pan out. I tried a new battery, but no luck there. In short, when the door opener light is on, the remote won't work. When it's off, the remote works fine.
Best Answer
CFL bulbs used in the opener cause signal blockage until fully lit. I don't know why but while the CFL bulb is flickering the signal gets blocked. After the bulb warms up, and stops flickering (about 30-60 seconds) your garage door remote should work fine. This can be tested easily enough. Does the remote open your door when you just get home and open door? Door opened because the light was off. But when you are leaving the garage, you use wall switch to open the door and can't close it by remote while trying to drive away. That's because the CFL bulb is still warming up after you just opened the door to leave. Easy solution is to change out CFL bulb with incandescent light (old style bulb with filament). I've heard that LED lights do this too, but my hunch is that some folks think CFLs are LEDs and are calling them by the wrong name. LEDs are instantly on and quite expensive, while CFLs flicker until warmed up and purchase price is pretty low. So change to incandescent in Door Opener and happy motoring. Appliance bulbs are perfect for Garage door Openers.