If your OBD2 scanner isn’t displaying any codes, despite suspecting a vehicle issue, several factors could be at play. One common reason is prematurely resetting the error codes before a state-required emissions inspection. Disconnecting the battery or using a reader’s reset button erases stored emissions parameters crucial for passing the inspection. These parameters are established through self-tests performed during each drive cycle, consisting of starting, driving, and shutting down the engine. Resetting them necessitates a new drive cycle, potentially requiring up to 50 miles of varied driving conditions to re-establish. Consequently, resetting before an inspection will likely result in failure.
Resetting codes might seem helpful if an inspection isn’t imminent. However, this action is only effective if the underlying issue causing the error has been resolved. Furthermore, “pending codes” can complicate matters. These codes indicate a corrected error, turning off the Check Engine Light (CEL), but require several drive cycles for confirmation. Many OBD2 scanners don’t differentiate between live and pending codes, potentially leading to confusion. A pending code may persist until the vehicle completes two or more drive cycles without the error recurring. Therefore, a seemingly empty scan result could indicate a pending code awaiting confirmation.
Resetting, whether manually disconnecting the battery or using the scanner, reverts learned emissions parameters to factory defaults. Various sensors, including coolant temperature, intake air temperature, and oxygen sensors, are continuously monitored. These sensors must operate within specific ranges to meet emissions standards. Data from these sensors is collected from ignition, throughout the drive cycle, and stored in the vehicle’s computer. This process takes time, explaining the need for extended driving to rebuild these parameters. Advanced OBD2 scanners offer readiness monitors, displaying which systems have passed or failed their tests, indicating readiness for emissions inspection with a “READY” or “NOT READY” status. This feature assists in determining if the vehicle is prepared for inspection.
