What is the purpose of Mode 4 in onboard diagnostics?

The purpose of Mode 4 in onboard diagnostics is specifically to erase diagnostic trouble codes (DTCs) from the vehicle's computer system. When a vehicle's onboard diagnostic system detects a problem, it generates codes that signify specific issues. These codes can be retrieved and interpreted to identify the nature of the problem. However, once the necessary repairs have been made, technicians can use Mode 4 to clear these trouble codes, which resets the system and allows it to begin monitoring for potential new issues. This step is crucial for ensuring that the check engine light or other warning indicators accurately reflect the current operating status of the vehicle after repairs are completed.

The other options, while related to vehicle diagnostics, serve different purposes. Monitoring vehicle performance is typically part of Modes 1 and 2, which display real-time data. Retrieving vehicle information pertains mostly to Modes 1 and 9, which show information about the vehicle's identification and performance metrics. Checking emissions compliance falls under Mode 6, which is focused on testing and verifying emissions-related functions of the vehicle.