05/07/2026 11:18 am
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Automotive Q&A
P0455 after a new fuel cap: smoke exits near the vent valve
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P0455 returned a week after a correct replacement fuel cap was installed. With low-pressure smoke connected at the service port, smoke comes freely from the vent outlet beside the charcoal canister. The hoses and canister shell are dry and undamaged, but the system will not build any indicated pressure.
I do not want to call the vent valve faulty just because smoke leaves an opening that may be normal with the key off. Does this system need the vent commanded closed during the test, and what should be checked if a scan-tool close command does not stop the flow?
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23/08/2026 12:11 pm
Yes—on many EVAP systems the canister vent is normally open with the key off, so smoke at the fresh-air outlet is expected until the valve is closed. Use the model-specific service test to command it closed, or isolate the vent only in the manner the procedure allows. Keep the test pressure within the stated low-pressure limit.
If flow continues after the close command, verify the command state in scan data, then test valve power, ground or driver control and inspect the sealing surface for dust. If the outlet seals, continue the smoke inspection around the rest of the system. An open vent during an uncommanded test is not, by itself, proof of a failed valve.
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24/08/2026 8:43 am
With the vent commanded closed, the outlet sealed and the system began to hold. Smoke then appeared at a short molded hose on top of the canister that had split beside its clamp. Replacing that hose fixed the leak, and the monitor completed on the next qualifying drive without resetting P0455.