Emissions: repair costs

Catalytic converters, oxygen sensors, EVAP and EGR parts. Typical ranges for the Boston area.

• Catalytic converter replacement$400 to $1,900. The catalytic converter cleans exhaust gases. A failed or clogged one causes codes like P0420, poor power, a rotten egg smell and a failed emissions test.
• Oxygen sensor replacement (one sensor)$110 to $370. An oxygen sensor reads the exhaust to help the engine mix fuel and air. Worn sensors cause a check engine light, poor mileage and emissions failures.
• EVAP purge valve replacement$85 to $260. The purge valve controls fuel vapor flow from the charcoal canister into the engine. A bad one causes EVAP codes, rough idle, or hard starts after fueling.
• EVAP vent valve replacement$120 to $360. The vent valve lets air into the fuel tank vapor system. A stuck one can cause EVAP codes, trouble filling the tank, and hard refueling.
• Gas cap replacement$5 to $110. A loose, worn or cracked gas cap is replaced. It is a common cause of EVAP codes and a check engine light.
• EGR valve replacement$160 to $760. The EGR valve sends some exhaust back into the engine to cut emissions. A clogged or stuck one causes rough idle, knock, hesitation and emissions codes.
• Secondary air injection (smog) pump replacement$270 to $1,175. The air pump blows fresh air into the exhaust at startup to cut emissions. A failed one sets codes and can fail an emissions test.

Other repair types

• Diagnostics
• Maintenance
• Brakes
• Battery, alternator and starter
• Engine, timing and cooling
• Ignition, fuel and air
• Suspension, tires and alignment
• A/C and heating
• Transmission
• ABS, airbag and electrical
• EV and hybrid

Typical range, estimate. Prices updated October 2026. Not a repair shop, estimates only.