I have a 2015 Chevy Silverado and recently changed the ECU. I'm now attempting to reprogram the key following the relearning steps, but the antitheft indicator light doesn't turn off even after waiting for 30 minutes with the key in the forward position.

If the anti-theft indicator light in your 2015 Chevy Silverado stays on after you’ve already tried reprogramming it by keeping the key in the forward position for 30 minutes, you might need to reattempt the process. Insert the key into the ignition and turn it to the 'on' position. The anti-theft light should appear and stay on for around 10 minutes. When the light turns off, switch the ignition to the 'off' position. Turn the key to 'on' once more and wait for roughly another 10 minutes until the light goes out again. Repeat this one final time. You're looking for any changes in the anti-theft light; it might go out entirely, flash once then turn off, or just flash. When you see this change, the reprogramming is complete. Turn the key back to 'off,' remove it for a few seconds, and then try starting your vehicle.