What indicates that a vehicle's emission system may have tampering issues?

The presence of non-factory components in a vehicle's emission system is a strong indicator that there may be tampering issues. Aftermarket parts may not comply with the same standards as original equipment manufacturer (OEM) components, potentially leading to increased emissions or failure to meet environmental regulations. The use of these non-factory parts can also compromise the integrity of the emission control system, making it difficult for the vehicle to function correctly in terms of pollution control.

Visible ID labels on parts typically indicate that they are from the manufacturer and often conform to specific emissions standards, which suggests they are likely compliant and not tampered with. Age-related wear on outdated parts might indicate a need for replacement but does not necessarily signify tampering. Similarly, recent maintenance records, while useful for tracking repairs, do not directly address whether the emission system has been altered or tampered with. Thus, the option highlighting non-factory components is the most significant red flag for potential tampering in a vehicle's emission system.