What should not be done when downloading new information to an ECM?

When downloading new information to an Engine Control Module (ECM), it is crucial to maintain a stable connection between the ECM and the diagnostic tool being used. Unplugging the data link during this process interrupts the communication, which can lead to incomplete downloads or corrupt data. This can potentially damage the ECM or lead to malfunctioning of the engine control system.

In contrast, ensuring that the data link is connected is necessary for the download to proceed. Leaving the key-switch on is typically recommended because it maintains power to the ECM during the update, preventing it from entering a low-power state which could interfere with the download process. Changing the computer settings should be done with caution and only if specified in the update process, but it should not occur while the download is in progress. Therefore, maintaining a stable and continuous connection is fundamental to successfully updating ECM information.