P0442 on GMC: How to Diagnose & Fix
Evaporative Emission Control System Leak Detected (Small Leak)
1 GMC model · 1 documented issue · $20-$250 repair
P0442 on GMC by model: symptoms, diagnosis and fix
P0442 on the Sierra 1500 is a small EVAP leak detected during the ECM's key-off/idle vacuum test. On these trucks the two most common real-world causes are a loose, worn, or cracked gas cap seal (the cheapest fix and always the first check) and — a documented GM issue (TSB 15-NA-019) — the fuel tank filler vent hose connector cracking, which allows vapor to escape and sets P0442 (and sometimes P0455). The vent hose fracture is addressed by replacing the vent hose assembly (part No. 22802073 on 2013-2015 models). The EVAP purge valve (engine bay) and vent solenoid (near the tank) can also weep. Drivers often notice a faint fuel odor and the CEL, with no drivability change.
Common Symptoms
- Check engine light
- Faint fuel/gasoline odor
- No drivability change
- Occasional failed emissions test
How to Fix
Start with the gas cap — inspect the seal and tighten/replace with OEM. If the code persists, perform a smoke test to pinpoint the leak; inspect the fuel filler vent hose connector for cracks and replace the vent hose assembly if fractured. Replace the purge or vent solenoid if the smoke test isolates it there.
Sources for this issue (1)
P0442 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0442 mean on a GMC?
P0442 stands for "Evaporative Emission Control System Leak Detected (Small Leak)." This emissions code means the evaporative emission (EVAP) control system has detected a small leak. The EVAP system seals the fuel tank and captures gasoline vapors, routing them to be burned in the engine instead of escaping into the air, and the computer periodically pressure- or vacuum-tests the system to confirm it's sealed. A small leak the size of about a 0.040-inch hole will set this code. By far the most common and cheapest cause is a loose, damaged, or missing gas cap, so that's the first thing to check, though any cracked hose or worn seal in the system can also trigger it. On GMC it is documented across 1 model: Sierra 1500.
What are the most common causes of P0442?
The most common causes of P0442 are: Loose, damaged, or missing fuel filler cap, Worn or cracked gas cap seal, Cracked or disconnected EVAP hose or line, Faulty purge valve or vent valve, Damaged O-ring or seal at the fuel tank or filler neck, Small crack in the charcoal canister, Leaking fuel tank sending unit gasket. The specific cause varies by vehicle.
How much does it cost to fix P0442 on a GMC?
Published repair estimates on GMC range from $20 to $250 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0442 on a different make?
View P0442 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.