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My engine light keeps coming on, what should I do?

The engine light on my 2012 Chevrolet Malibu keeps coming on with code P0455 (Evaporative Emission Control System leak). I have already replaced my fuel cap – can you offer any suggestions – Kori

The Evaporative Emission Control System (EVAP) is designed to capture fuel-tank vapour, store it in a charcoal canister and redistribute it into the engine to be burnt.

When a code P0455 appears, the Powertrain Control Module has detected a large leak present in the EVAP system. The most common fix is replacing the leaking gas cap; however, when the code persists, a deeper analysis has to be carried out.

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What you can do at home: Check for corrosion at the fuel filler neck that might affect the seal of the gas cap. Then, examine the visible part of the filler neck, looking for further corrosion that might allow vapour to escape from it and the venting tube. Underneath the car, are there any signs gas is leaking from the tank?

At the shop: Another common vapour-leak point on the Malibu resides within the charcoal canister and its canister-purge valve. A technician uses a smoke machine to aid with the diagnosis by injecting smoke into the EVAP system while opening and closing the purge valve using a scan tool. This enables the technician to get a close-up look underneath the vehicle at these two components, with a high-powered light following the trail of smoke, hopefully verifying the leaking component(s).

Lou Trottier is owner-operator of All About Imports in Mississauga. Have a question about maintenance and repair? E-mail globedrive@globeandmail.com, placing "Lou's Garage" in the subject area.

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