P0442: Evaporative Emission System Leak Detected (Small Leak)

What does P0442 mean?

To check the EVAP system, the ECM seals it and watches pressure or vacuum. If it changes faster than expected, there is a leak.

P0442 is the small leak version of this test. It sits between P0455 (large leak) and P0456 (very small leak). The exact leak size and test method depend on the vehicle.

Common symptoms

• Check engine light on
• Usually no change in how the car drives
• Possible faint fuel smell

Common causes

The causes below are the ones commonly seen with P0442. The actual cause can vary by vehicle, engine and mileage, so treat this list as a starting point, not a diagnosis.

• A loose, worn or damaged fuel cap
• A small crack or loose connection in an EVAP hose
• A leaking purge valve or vent valve
• A faulty leak detection pump on some vehicles

What to check with a scanner

• Inspect the fuel cap seal and make sure it clicks.
• Look over EVAP hoses and connections near the engine and tank.
• After a repair, clear the code and use the readiness screen to see when the EVAP monitor runs again.
• A smoke test is the standard way to find small leaks.

How to read and clear P0442 with OBD Master Pro

1. Plug in your adapter. Connect a generic ELM327 (or ELM329) OBD2 adapter to the diagnostic port, usually under the dashboard on the driver's side. Bluetooth Classic, Bluetooth LE, Wi-Fi and USB OTG adapters are supported.
2. Switch the ignition on. Turn the key to ON or start the engine, depending on your car.
3. Connect in OBD Master Pro. Open the app, go to Connection and pick your adapter. Classic Bluetooth adapters connect from the Bluetooth tab, Bluetooth LE adapters from the BLE tab with no pairing needed. Use the generic OBD2 / EOBD profile or your car's brand profile.
4. Read the codes. Open the fault codes screen to see stored, pending and permanent codes. Confirm P0442 is listed and note any other codes, since they often explain the cause.
5. Check the details. Look at freeze frame data, Live data and, where your car supports it, Mode 06 test results (see the checks above).
6. Fix, then clear. After the repair, clear the codes to turn off the check engine light. Clearing also resets the emissions readiness monitors, so drive normally and check the readiness screen before any inspection. Permanent codes cannot be erased with a scan tool; they clear on their own once the car's self test passes.

Tip: you can also look up P0442 and other codes in the app's DTC search without connecting to a car. If your adapter will not connect, use Connection > Share connection log and email it to support. Many cheap ELM327 clones only handle basic engine OBD2, which is all you need for P0442.

When to see a mechanic

Get professional help if any of these apply:

• The code returns after replacing the gas cap
• You need a smoke test to find the leak
• Several EVAP codes are stored

If you are unsure, a qualified technician can confirm the cause with tests such as smoke testing, pressure testing or scope readings. Clearing a code does not repair the fault.

Related trouble codes

See all OBD2 trouble code guides

Related guides

Check engine light on: what to do · How to read an OBD2 code (P, B, C, U) · Stored, pending and permanent codes and freeze frame · OBD2 readiness monitors explained · OBD2 glossary · OBD2 by car brand