Can a loose gas cap cause P0442?

Yes. A loose, cracked, or missing fuel cap is a common cause of P0442. The EVAP system is sealed, and even a slight gap at the cap allows vapours to escape. Always tighten the cap until you hear it click and replace it if the seal is worn.

What is the difference between P0442 and P0455?

Both indicate EVAP system leaks, but P0442 is a small leak (less than about 1mm equivalent orifice) while P0455 is a large leak. Small leaks are often from deteriorated hoses or a worn cap seal. Large leaks suggest a disconnected hose or missing cap.

Will P0442 go away on its own?

If the cause was a loose fuel cap and you tighten it properly, the ECU will eventually clear the code after several successful EVAP system tests during normal driving. This may take 3-5 drive cycles. You can also clear it with a scanner.

It is not mechanically serious and will not damage your engine or affect performance. However, it means fuel vapours are escaping into the atmosphere, and a lit check engine light with a stored emissions code is what gets a car rejected at inspection.

How does the EVAP system detect a small leak?

Most modern vehicles use either a vacuum-based test or a dedicated leak detection pump. The system seals itself and applies a slight vacuum or pressure, then monitors whether it holds. A small drop indicates a leak, and the ECU sets P0442.

P0442: Evaporative Emission System Leak Detected (Small Leak)

Quick Answer

Safe to drive (short-term)

P0442 means the engine control unit has detected a small leak in the evaporative emission control system. This system captures fuel vapours from the tank and routes them to the engine to be burned. A small leak allows vapours to escape, increasing hydrocarbon emissions.

Severity: Low · EVAP System
Estimated repair cost: From €10 to €450+, varies by vehicle

Scan your own car in about 60 seconds: see whether P0442 is really what it has, how urgent it is, and what the fix should cost. Free on iPhone and Android with an ELM327 adapter (Bluetooth LE on iPhone).

Get Skanyx free

What does P0442 mean?

P0442 is a evap system-related diagnostic trouble code classified as low severity. When your vehicle's ECU detects this condition, it stores P0442 and illuminates the check engine light.

Where it is on the car

Fuel filler cap
Fuel tank pressure sensor
Charcoal canister
Vent valve (to fresh air)
Purge valve
Intake manifold and engine

A leak can be anywhere in this system: the cap, a hose, the canister or a valve. The cap and the vapour hoses are marked. The cap is the cheapest and quickest thing to check first.

What are the symptoms of P0442?

If your vehicle has triggered P0442, you may notice one or more of these symptoms:

Check engine light on
Faint fuel smell near the vehicle, especially in warm weather
Failed emissions test
No noticeable driveability symptoms in most cases
Fuel cap warning light on some vehicles

What causes P0442?

Here are the most common causes of P0442:

Loose, damaged, or missing fuel cap
: high
Cracked or deteriorated EVAP hoses
: high
Faulty purge valve (stuck open)
: medium
Leaking charcoal canister
: medium
Damaged fuel tank filler neck or seal
: low

Is it safe to drive with P0442?

Generally yes, for short-term driving. A small EVAP leak does not affect engine performance or safety. You can drive normally, but repair before your next emissions inspection. A loose fuel cap is a common cause and the first thing to check.

How do you diagnose P0442?

Follow these steps to pinpoint the root cause of P0442:

Check the fuel cap first. Remove it, inspect the rubber seal for cracks or debris, and re-seat it until it clicks. Clear the code and drive for a few days to see if it returns
Visually inspect all EVAP hoses from the fuel tank to the charcoal canister and from the canister to the purge valve at the engine. Look for cracks, loose clamps, or disconnections
Perform a smoke test on the EVAP system by sealing the system and introducing smoke. Watch for smoke escaping at hose connections, the canister, or the fuel tank area
Test the purge valve and vent valve by commanding them open and closed with a diagnostic tool that supports actuator tests (on many cars this needs manufacturer-level software, not a generic OBD2 reader). A stuck-open purge valve can allow ambient air into the system, mimicking a leak
If the smoke test reveals no external leaks, inspect the charcoal canister for cracks and the fuel tank for damage, particularly around the fuel pump module seal

How much does P0442 cost to fix?

Repair costs for P0442 vary depending on the root cause and your vehicle. Here are typical estimates:

Repair	Parts Cost	Labor Cost	Total Estimate	DIY Difficulty
Replace fuel cap	€10–€40	€0–€0	€10–€40	Easy
Replace EVAP hose(s)	€10–€60	€40–€150	€50–€210	Moderate
Replace purge valve or vent valve	€20–€100	€30–€120	€50–€220	Moderate
Replace charcoal canister	€60–€250	€60–€200	€120–€450	Moderate

Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.

Full repair guides

EVAP Purge Valve Replacement Cost

P0442 on specific vehicles

P0442 behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:

P0442 on Volkswagen

Volkswagen Golf

See Volkswagen-specific causes & cost

P0442 on BMW

BMW 3 Series

See BMW-specific causes & cost

P0442 on Ford

Ford Focus

See Ford-specific causes & cost

Toyota

Toyota Yaris

2006-2024

On a Yaris with a screw-on fuel cap, a worn cap seal is a cheap first thing to rule out for P0442. If a new cap does not cure it, the EVAP hoses, purge valve and canister need checking with a smoke test like on any other car.

These codes are often seen alongside P0442 or indicate related issues:

Common questions about P0442

Can a loose gas cap cause P0442?: Yes. A loose, cracked, or missing fuel cap is a common cause of P0442. The EVAP system is sealed, and even a slight gap at the cap allows vapours to escape. Always tighten the cap until you hear it click and replace it if the seal is worn.
What is the difference between P0442 and P0455?: Both indicate EVAP system leaks, but P0442 is a small leak (less than about 1mm equivalent orifice) while P0455 is a large leak. Small leaks are often from deteriorated hoses or a worn cap seal. Large leaks suggest a disconnected hose or missing cap.
Will P0442 go away on its own?: If the cause was a loose fuel cap and you tighten it properly, the ECU will eventually clear the code after several successful EVAP system tests during normal driving. This may take 3-5 drive cycles. You can also clear it with a scanner.
Is P0442 serious?: It is not mechanically serious and will not damage your engine or affect performance. However, it means fuel vapours are escaping into the atmosphere, and a lit check engine light with a stored emissions code is what gets a car rejected at inspection.
How does the EVAP system detect a small leak?: Most modern vehicles use either a vacuum-based test or a dedicated leak detection pump. The system seals itself and applies a slight vacuum or pressure, then monitors whether it holds. A small drop indicates a leak, and the ECU sets P0442.

Read our detailed guides

Scan your car with Skanyx to diagnose P0442

Your car logged P0442. Skanyx reads it on a standard OBD2 adapter (Bluetooth LE on iPhone), tells you whether it is safe to keep driving, and shows the €10-€450 repair range so you know the number before a shop quotes you. Free on iPhone and Android, and you do not need to be a mechanic to read it.