What Does Inc Mean On A Code Reader

Overview

On an OBD-II (On-Board Diagnostics II) code reader, the abbreviation ‘INC’ stands for ‘Incomplete’. It appears in the context of the vehicle’s emissions monitor readiness status. Modern vehicles have multiple onboard diagnostic monitors that continuously or periodically test various emissions control systems, such as the catalytic converter, oxygen sensors, and evaporative emissions system. When a monitor has not yet completed its diagnostic self-test during the current driving cycle, the code reader displays ‘INC’ for that monitor. This status is a normal part of the vehicle’s self-diagnostic process and does not necessarily indicate a malfunction.

History / Background

The OBD-II standard was introduced in the mid-1990s in the United States, mandated for all light-duty vehicles from 1996 onward. The system was designed to monitor emissions-related components and alert the driver via the check engine light when a fault is detected. As part of the standard, vehicle manufacturers implemented a set of ‘monitors’ that run specific tests under certain driving conditions. The readiness status of these monitors—whether they have completed their test (OK/Ready) or not (INC/Not Ready)—became a key part of emissions inspection programs. The term ‘INC’ is a shorthand used by many code readers to denote that a monitor’s test has not been completed, often because the vehicle has not been driven under the necessary conditions (e.g., specific speed, load, temperature) for the monitor to run.

Importance and Impact

The ‘INC’ status is critical for vehicle emissions testing and state inspections. In many jurisdictions, a vehicle must have a certain number of monitors showing ‘Ready’ (i.e., not ‘INC’) to pass an OBD-II emissions test. If too many monitors are incomplete, the vehicle may fail the inspection even if no diagnostic trouble codes (DTCs) are present. This requirement ensures that the vehicle’s self-diagnostic system has had a chance to verify the proper operation of emissions components. For mechanics and vehicle owners, understanding ‘INC’ helps in diagnosing why a vehicle might not pass an inspection and guides them to perform the necessary driving cycles to complete the monitors.

Why It Matters

For anyone using a code reader—whether a professional mechanic, a DIY enthusiast, or a vehicle owner preparing for an emissions test—seeing ‘INC’ on the screen is a common occurrence. It matters because it indicates that the vehicle’s diagnostic system has not yet fully evaluated all emissions systems. Drivers may need to follow specific drive cycle procedures to allow the monitors to run and change their status from ‘INC’ to ‘Ready’. Failing to do so can lead to a failed emissions test, even if the vehicle is mechanically sound. Additionally, after clearing DTCs or resetting the ECU, all monitors typically reset to ‘INC’ until the vehicle is driven sufficiently. Recognizing this helps avoid unnecessary repairs or confusion.

Common Misconceptions