What this code means
P0442 may mean the EVAP system is seeing a small fuel vapor leak during a monitor check.
What the vehicle may do
- The vehicle may only show a check engine light.
- The engine may often run normally even with this code stored.
- Fuel odor may be possible depending on where a leak is located.
Possible fault areas
- Possible filler cap or capless filler sealing concern.
- Possible loose, damaged, or misrouted EVAP vapor hose or line.
- Possible purge-side or vent-side EVAP sealing concern.
- Possible EVAP canister, fuel tank, or filler pipe area leak.
- Possible debris or contamination around the EVAP vent inlet or filler seal.
Diagnostic path
Open: what P0442 means
On this F-150, P0442 means the PCM may be seeing a small fuel vapor leak during the EVAP running loss monitor. The driver may only notice a check engine light, and the truck can otherwise feel normal. The broad fault areas often include the fuel filler sealing area, capless filler pipe or cap if equipped, vapor hoses and lines, the purge and vent side of the EVAP system, the canister area, or contamination around the vent inlet. We’re going to keep this diagnosis ordered: prove the fault with the scan tool first, inspect the obvious sealing and hose concerns, then use smoke and pressure testing only when the earlier checks don’t find it.
Safety and test setup reminders
Before disconnecting any fuel tubes or fuel system components, relieve fuel system pressure. Fuel can stay under high pressure even with the engine off, and accidental spray is a serious injury risk. Handle fuel with normal fuel-spill precautions and keep ignition sources in mind. If you’re using the EVAP leak detector with onboard nitrogen generator, make sure the fuel tank is less than 85% full. Also, do not apply smoke to the EVAP leak detection control module, because that can damage the module. Soap solution around the filler cap or capless filler pipe, and using a hydrocarbon analyzer to find this EVAP leak, are not recommended here.
Start with the scan-tool EVAP test
Start with the scan-tool EVAP leak test. On hybrid applications, run the KOEO EVAP leak test. On all others, run the PCM evaporative emissions system test. If that scan-tool test is not available, move on to the next diagnostic step. If the test passes for P0442, the system is operating correctly at this time. Clear the PCM DTCs and repeat the self-test. If the test does not pass, continue by checking codes.
Check codes, then stay on the P0442 path
Next, check for DTCs. If other EVAP faults are present, let the code direction guide the next move instead of guessing. For P0442, continue into the visual and purge-check portion of the path. If none of the listed EVAP codes are present, the direction changes into a symptom-based path, so pause there and recheck the earlier diagnostic path before moving forward.
Inspect the filler area, hoses, lines, and purge operation
Now do the hands-on visual check. Look over the capless fuel tank filler pipe or fuel cap if equipped, and inspect the EVAP lines and hoses for damage or incorrect connections. For P0442, pay close attention to the filler sealing area, loose or damaged vapor hoses, and debris or contamination around the canister inlet, vent valve filter, and vent hose assembly. If it has a capless filler, cycling the supplemental fueling adapter in and out five times can help clear debris from the seal. Then run the scan-tool purge check for the application. If you find a concern, repair as necessary, clear the PCM DTCs, repeat the self-test, and rerun the EVAP leak test. If no concern is found for P0442, move into leak-detector hookup.
Hook up the EVAP leak detector
With the ignition off, connect the EVAP leak detector with onboard nitrogen generator, or an equivalent tool. Set it up according to the tool maker’s setup information. Disconnect the fuel vapor-to-EVAP canister line at the EVAP canister purge valve, then connect a suitable hose adapter to that fuel vapor line connection. Once the hookup is complete, choose the next step based on what you’re doing: leak detection goes to the smoke test, and leak repair verification goes to the pressure test. If the hookup is not complete, stop and sort out the tool setup before continuing. Also remember, smoke and airflow from this tool will not pass through liquid fuel, and liquid fuel may be present in the filler pipe.
Smoke test to locate the leak
For leak detection, carry out the Phase 2 smoke test. Remove the fuel filler cap, or install the supplemental refueling adaptor. Connect the supply hose into the hose adapter and set the leak detector to SMOKE. Turn the ignition on, access the PCM, and control the EVAPCV PID. Close the EVAP canister vent valve by commanding the EVAPCV PID ON at 100% duty cycle, then start the smoke supply. First verify the connection at the fuel vapor-to-EVAP canister line at the purge valve is not leaking. If smoke does not exit the fuel tank filler pipe after the system is pressurized, command the vent valve open. Once smoke is seen at the vent valve, command it closed again. When smoke exits the fuel tank filler pipe, install the fuel filler cap or remove the supplemental refueling adaptor. Keep applying smoke, use the halogen spotlight along the EVAP system path, and look for smoke escaping at the leak. Work the hoses, valves, canister, tank, filler pipe, filler inlet, and nearby connections while watching for smoke. If no smoke shows up, visually inspect the filler pipe and filler sealing area, because pressure may not push smoke to every leak in that section. If you locate the leak, repair as necessary, reconnect everything that was disconnected, run the scan-tool EVAP test again, and then move to pressure verification. If the leak is not located, connect everything back up and continue with the pressure verification test.
Verify the leak with the pressure test
For verification, carry out the Phase 1 leak verification pressure test. Calibrate the flowmeter using the 0.020 standard. Connect the supply hose to the vehicle through the hose adapter, and set the leak detector to the 0.020 standard. Turn the ignition on, access the PCM, and control the EVAPCV PID. Close the EVAP canister vent valve by commanding the EVAPCV PID ON at 100% duty cycle. Start the pressure supply. The flowmeter ball should start all the way at the top; keep pressurizing the EVAP system until the ball stops descending. Once it stops, compare the ball position to the red pointer flag. If the system passes this leak verification pressure test for P0442, no concern is present at that point. Clear the PCM DTCs and repeat the self-test. If it does not pass, go back to the smoke test and continue looking for the leak.
Close
The key with P0442 is to avoid jumping straight to parts. Confirm the fault, inspect the common sealing and hose areas, use smoke to find the leak, and use the pressure test to verify the repair and confirm the code stays gone. For more diagnostic training, visit stepdiagnostics.com.
Final check
P0442 is best approached by confirming the monitor result, inspecting common EVAP sealing areas, locating any leak with smoke, and verifying with the pressure test.
For more guided automotive diagnostics, visit STEP Diagnostics.
