Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Monitored Emission Control Systems
The OBD-II system monitors all emission control systems that are on-board. Not all vehicles have a full complement of emission control systems. For example, a vehicle may not be equipped with AIR or EGR. The OBD-II regulations require monitoring of the following:
- Air Conditioning system.
- Catalytic converter efficiency.
- Comprehensive component monitoring - emission related inputs and outputs.
- Evaporative Emissions (EVAP) system.
- Exhaust Gas Recirculation (EGR) system.
- Fuel delivery system.
- Heated catalyst monitoring.
- Misfire monitoring.
- Oxygen Sensor (O2S or HO2S) system.
- Oxygen Sensor heater (HO2S Heater) system.
- Secondary Air Injection (AIR) system.
For the specific DTCs required for each system, refer to INSPECTION/MAINTENANCE SYSTEM DTCS . Systems such as fuel delivery, misfire, and comprehensive components may not be listed in a system status list. These tests run continuously on some vehicles and may not require an indicator.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.