In Honda vehicles, the “Check Emission System” warning signals a fault in the emissions-control system or a pending diagnostic code detected by the car’s onboard computer (OBD-II).
It can appear for a range of reasons—from a loose fuel cap to more substantial issues like sensors, the EVAP system, or the catalytic converter. When it lights up, the engine may run differently and the vehicle may fail an emissions test until the fault is diagnosed and repaired.
What this warning means
The phrase is generated by Honda’s onboard diagnostic system when an emissions-related component or monitor detects a fault. It typically triggers the Malfunction Indicator Lamp (MIL) on the instrument cluster and can accompany stored diagnostic trouble codes (DTCs) that point to the specific issue.
Common causes of the Check Emission System warning
The following issues are commonly associated with this warning across many Honda models. They can range from minor to serious and may trigger codes stored in the OBD-II system.
- Loose or damaged gas cap, allowing EVAP leaks and fuel vapor escape
- EVAP system leaks or a faulty purge valve/canister
- Faulty oxygen sensors (O2 sensors) or downstream sensors affecting the air-fuel mixture
- Malfunctioning catalytic converter or exhaust restrictions
- Vacuum leaks or cracked hoses impacting engine emissions
- Mass airflow sensor (MAF) issues or other sensor faults
- EGR (exhaust gas recirculation) valve or gasket problems
- Pending or active diagnostic trouble codes (DTCs) stored by the OBD-II system
Conclusion for this list: Emissions-system faults cover a broad spectrum, from simple fixes to more involved repairs requiring professional servicing.
How to diagnose and fix the Check Emission System warning
Following steps can help identify the source and guide appropriate action. Some fixes are quick and low-cost, while others may require professional diagnostic equipment and service.
- Check the gas cap: ensure it is tightened to the click and in good condition; drive for a few cycles to see if the warning resets.
- Pull the codes with an OBD-II scanner: read the stored DTCs to identify the likely system or component involved.
- Inspect the EVAP system for leaks: look for cracked hoses, loose connections, or a faulty purge valve and canister.
- Inspect oxygen sensors and MAF sensor: check for sensor faults, wiring damage, or contamination; replace sensors as recommended by Honda service data.
- Assess the catalytic converter and exhaust system: determine if there are restrictions or degradation affecting emissions performance.
- Check the EGR valve and related components: clean or replace if it’s stuck or malfunctioning.
- Look for service bulletins or recalls: software updates or component replacements may address known emission-related issues.
- Seek professional diagnostic if codes point to complex issues or the light remains on after a reset.
Conclusion: A methodical approach—starting with quick checks and progressing to diagnostic testing—helps determine whether the issue is a minor fix or requires more extensive repair to restore emissions performance and pass inspections.
Summary
The “Check Emission System” warning on a Honda signals an emissions-control fault or a detected diagnostic code. Causes can range from a loose gas cap to faulty sensors, EVAP leaks, EGR problems, or catalytic converter issues. Start with basic checks, retrieve OBD-II codes, and pursue professional service if the issue persists or involves critical components. Addressing the problem promptly helps protect the environment, maintain engine performance, and ensure compliance with emissions tests.