P0442
Evaporative Emission Control System Leak Detected (small leak)P0442 is a generic OBD-II powertrain diagnostic trouble code: Evaporative Emission Control System Leak Detected (small leak). It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0442 means
P0442 is an SAE generic OBD-II diagnostic trouble code that indicates the powertrain control module (PCM) has detected a small leak in the evaporative emission control (EVAP) system. The EVAP system captures fuel vapors from the fuel tank and routes them through a charcoal canister, then purges them into the intake manifold to be burned during normal engine operation, preventing raw hydrocarbons from escaping into the atmosphere. A small leak is defined as an opening of approximately 0.020–0.060 inches (0.5–1.5 mm) — roughly the size of a pin prick — which causes the system to fail its vacuum-retention self-test.
The PCM monitors the EVAP system by commanding the vent valve closed and the purge valve open (or by using a dedicated leak detection pump on some platforms), then watching for vacuum decay over a set time window. When pressure or vacuum bleeds off faster than the calibrated threshold, P0442 is stored and the malfunction indicator lamp (MIL) is illuminated. Because the leak is small, drivability is rarely affected, but fuel vapour is continuously venting into the atmosphere and the vehicle will typically fail a tailpipe or OBD emissions inspection.
The most common root cause is a loose, cracked, or worn fuel filler cap, which accounts for a significant proportion of P0442 cases and can be ruled out first at no cost. Beyond the cap, deteriorated EVAP hoses and a failed purge or vent control valve are the next most frequent culprits. Accurate diagnosis almost always requires a smoke machine to pressurize the system and locate the exact leak point, as the small orifice size makes visual inspection unreliable.
Common causes
Most-frequently reported root causes when P0442 is logged.
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1
Loose, cracked, or improperly seated fuel filler cap
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2
Deteriorated or disconnected EVAP system hose or tubing
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3
Faulty or stuck-open EVAP purge control valve
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4
Faulty or stuck-open EVAP vent control valve
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5
Cracked or damaged charcoal canister
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6
Damaged or pinhole-leaking fuel tank
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7
Defective fuel tank pressure (FTP) sensor giving false readings
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8
Failed EVAP leak detection pump (LDP) on equipped vehicles
Symptoms drivers notice
How to diagnose P0442
A typical diagnostic flow when this code is present.
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1
Retrieve and record all stored DTCs and freeze-frame data with an OBD-II scan tool before clearing
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2
Inspect the fuel filler cap — check for cracks, damaged O-ring, or improper torque; tighten or replace and retest
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3
Visually inspect all accessible EVAP hoses, tubes, and the charcoal canister for cracks, kinks, or disconnected fittings
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4
Perform a smoke-machine test: seal the EVAP system, introduce low-pressure smoke, and trace any visible leak to its source
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5
Use a scan tool to command the EVAP purge valve open and closed while monitoring live data; verify it seals properly with a vacuum pump
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6
Command the vent valve closed with a scan tool and apply vacuum to confirm it holds; replace if it bleeds down
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7
Check fuel tank condition for deformation or pinhole corrosion if no leak is found in the upper EVAP plumbing
Related powertrain codes
- P0400 — Exhaust Gas Recirculation Flow Malfunction
- P0401 — Exhaust Gas Recirculation Flow Insufficient Detected
- P0402 — Exhaust Gas Recirculation Flow Excessive Detected
- P0403 — Exhaust Gas Recirculation Circuit Malfunction
- P0404 — Exhaust Gas Recirculation Circuit Range/Performance
- P0405 — Exhaust Gas Recirculation Sensor A Circuit Low
Frequently asked questions
Is it safe to drive with a P0442 code?
Yes, in most cases. P0442 rarely causes drivability problems or immediate mechanical damage. The vehicle can be driven short-term, but the leak allows fuel vapours to escape into the atmosphere and will likely cause a failed emissions test, so the fault should still be repaired promptly.
Can a loose gas cap really trigger P0442?
Yes, and it is the single most common cause. Even a cap that feels snug may have a cracked body or a worn O-ring that prevents a proper seal. Always inspect and re-torque or replace the cap first — it takes seconds and costs nothing or about $10 for a new cap.
What is the difference between P0442 and P0455?
Both codes relate to EVAP system leaks, but P0442 indicates a small leak (approximately 0.020–0.060 inches) while P0455 indicates a gross or large leak. P0442 is harder to locate and almost always requires a smoke machine; P0455 leaks are often large enough to detect by smell or visual inspection.
Why does P0442 come back after I cleared it and replaced the gas cap?
If the code returns after a new cap is fitted, the leak source is elsewhere in the EVAP system — most often a cracked hose, a failed purge or vent valve, or a damaged charcoal canister. A professional smoke test is the fastest way to pinpoint the exact location of a small leak that visual inspection cannot reliably find.
Disabling P0442 in software
RaceTune can permanently disable P0442 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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