1999 LS1 P0442 Small EVAP Leak
P0442 means the sealed EVAP system failed the PCM leak test. It does not identify the leaking part.
What the PCM is testing
- Whether the system can pull the expected vacuum.
- Whether the sealed system can hold that vacuum.
- Purge and vent valve operation.
- Fuel-tank pressure feedback.
Start with failure records
Save freeze-frame/failure information and note fuel level, temperature and operating state. EVAP diagnostics only run when their enable criteria are satisfied.
Physical branch
- Fuel cap sealing surface and correct cap.
- Vapor, purge and vent hoses for disconnects, splits, pinches or blockage.
- Canister and valve connections.
Control branch
Prove the purge and vent valves can create and seal the system, and verify the tank-pressure signal responds plausibly. A smoke test alone does not prove the PCM can execute its commanded vacuum test.
Modified-car branch
Fuel-cell, tank, vent, purge or engine-swap changes can invalidate the stock routing. Diagnose the plumbing that is actually installed.
DO NOT REPLACE YET
Do not replace the purge valve, vent valve, tank-pressure sensor or charcoal canister only because P0442 is stored. First prove which part of the vacuum-and-hold test fails.
AFTER THE FAILURE IS PROVEN
Use the proven failed branch—not the original symptom—to choose the replacement. Go from diagnosis to the Parts Verdict →