P0442

What This Code Means

P0442 indicates a small leak in the evaporative emission control system (EVAP). The EVAP system keeps fuel vapors out of the atmosphere by routing them from the fuel tank to the intake manifold to be burned. The diagnostics flag a leak above the allowable threshold—usually a hole 0.02–0.04 in in diameter. The most common causes are a loose or faulty fuel filler cap, cracked EVAP hoses, or a bad purge valve. On a BMW, the filler cap is the most likely culprit.

Symptoms

• Warning lights: The check engine light (CEL) comes on.
• Smell: A fuel odor is possible.
• Behavior: The code has no effect on handling or performance.

Diagnosis and Repair

Step 1: Check the Fuel Filler Cap

• Tighten the cap until it clicks. If a loose cap caused the code, it won't return after you clear it.
• Inspect the sealing ring for damage. Replace the cap if needed (genuine BMW part 16117224045).

Step 2: Smoke Test

• If the code comes back, smoke-test the EVAP system with dedicated equipment—that pinpoints the exact leak location.
• Check the EVAP hoses for cracks and loose connections.

Step 3: Test the Purge Valve

• The purge valve (genuine BMW part 13907640940) can stick or fail to seal when closed. Test it with ISTA or a multimeter.

Step 4: Clear Codes and Test Drive

• After the repair, clear the codes and take a test drive to verify.

What Happens If You Ignore It

A small leak left unattended can let moisture and dirt into the fuel system, which can lead to fuel pump or injector failures. A faulty EVAP system will also fail the emissions test (state inspection). Caught early, the repair usually amounts to a new cap or hose—a neglected leak can mean replacing the charcoal canister and other components.