ADylan: 2003 Chevy Impala, no crank, no start after replacing the key cylinder, it was starting fine until the key cylinder went bad.
Sparky: The lock cylinder assembly has an anti theft sensor built into it and now that you have replaced the lock cylinder assembly it needs to relearn the new sensor value. In most instances a manual relearn is possible but in some cases a software command is needed.
The manual procedure is as follows.
Start with a fully charged battery and connect a battery charger if needed to maintain battery voltage. The ignition will be on for at least 10 minutes but may be on for an hour. If that battery voltage falls too low the procedure will not work and will have to be restarted.
Try to crank the engine and leave the key in the run position. The theft or security light should be on or flashing. At about the ten minute mark the light will either go out or stop flashing. Turn the ignition off for 10 seconds then try to restart the engine. This process may need to be repeated for up to four times before the engine will actually fire up and run. If the engine does not run do not turn the ignition off. Keep it on until the security light goes off or stops flashing ans keep repeating the process.
ADylan: It took a while and was very worried. It took all four tries but it finally started. Thanks