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2004 Chevrolet Trailblazer LS P0455 Code: Diagnosis and Fix After Smoke Test and EVAP System Repairs

Model: 2004 Trailblazer LS Fault Code: P0455 Posted: 2015-08-10 13:44

I recently encountered a P0455 diagnostic code on my 2004 Chevrolet Trailblazer LS with a 4.2L V6, automatic transmission, and 4WD. I've already replaced the purge solenoid, vent valve, charcoal canister, and gas cap. A professional smoke test was performed and showed no visible leaks. The only remaining step I'm considering is disconnecting all EVAP lines and blowing them out with compressed air—would this resolve the issue or am I missing something? Any insights would be greatly appreciated. I also noticed that during the smoke test, the system had to be activated to working status; otherwise, the smoke bypassed through the vent valve. This suggests a potential issue with the vent control mechanism or sensor response.

Related fault codes
P0455
Comments (5)
Anonymous 2015-08-10 14:27

P0455 typically indicates a significant evaporative emissions leak—could it be intermittent, such as a stuck-open vent or purge solenoid? Has any other diagnostic trouble code (DTC) been triggered? Did you check the freeze frame data for the event that generated the P0455? Have you performed repairs related to the fuel pump or sending unit? Instead of blowing out the lines, try using an OBD2 scanner to command the EVAP system and monitor FTP sensor readings while manually shaking the EVAP lines. Additionally, during a smoke test, ensure the system is fully pressurized—observe the smoke machine flow rate. In a sealed system, no flow should be detected; if there's flow, it may indicate a leak. Also, note that the top of the fuel tank and filler tubes are often hidden, so visibility can be limited.

Anonymous 2015-08-10 16:09

During our smoke test, we raised the vehicle on a hoist to get better access to the fuel tank and all EVAP lines. Nothing appeared visibly compromised. No repairs have been done to the fuel pump or sending unit—this vehicle has only 84,200 miles on it and has generally performed well. The system required activation to reach working status during testing; otherwise, smoke would bypass through the vent valve. This behavior may point to a faulty vent control or sensor issue. I hope this helps—thank you for the advice.

Anonymous 2015-08-11 09:25

Yes, you must enter test mode to close the vent valve during a smoke test. Many smoke machines have flow meters—under normal conditions, a sealed system should show zero flow. If there's flow, it indicates a leak. In such cases, the FTP sensor should read a fixed voltage. This is a key indicator for diagnosing EVAP leaks when smoke testing fails to reveal them.

Anonymous 2015-09-03 19:28

Update on my P0455 issue: I found a service bulletin specific to this model year and trim that recommends manipulating or moving the filler neck and EVAP lines during the smoke test. After performing a second smoke test with these adjustments, no leaks were detected. I then took it to a Chevrolet dealership for diagnostics, where they identified a malfunctioning fuel pressure sensor located in the fuel tank. Replacing this component resolved the issue completely. Thanks for all the helpful suggestions!

Anonymous 2015-12-02 08:35

The electrical connections controlling EVAP components may be faulty. Try cleaning both sides of the connectors and verify continuity between points—especially for grounding issues. If no leak is detected during a smoke test, it's unusual unless the leak is intermittent or only occurs when driving. This could suggest a mechanical or electrical fault not visible under static conditions.