Fault code P0442 – a step-by-step guide to diagnosing and fixing it

P0442 is registered when the powertrain control module detects a small fuel vapour leak in the evaporative emission control (EVAP) system, activating the check engine light. When the vehicle is switched off, the module tests for leaks by closing the control valves and thereby sealing the system. If the pressure is not maintained, it indicates that there is a hole or crack somewhere. This DTC is triggered for small to medium-sized leak holes with a diameter of around 0.02” - 0.04”.

• A faulty purge flow solenoid or valve vent control solenoid. For example, the valve components may be affected by the gradual build-up of charcoal from the canister, carbon deposits and other impurities, causing them to wear or jam. Vapours may also be able to leak through due to damaged seals in the system.
• A leaking charcoal canister or fuel tank leak. Cracks may start to appear and parts can corrode over time.
• A loose, damaged or missing fuel cap of the car. Without a proper cap, the vapours will be able to escape through the filler neck.
• Holes or cracks in the EVAP hoses. This can occur if the parts are not installed properly or are incompatible with the vehicle.

• Activation of the check engine light
• Decreased fuel efficiency
• A fuel smell while the vehicle is stationary
• An increase in emissions
• A rough or erratic idle

• Check the DTCs using a diagnostic scanner to verify which faults have been detected by the control unit. P0442 may be accompanied by codes P0440, P0441 or P0446, which usually indicate a solenoid malfunction or canister leak.
• The solution to the fault may be as simple as replacing the cap on the fuel tank in the car. Check the cap for signs of damage and make sure it is tightened properly. It might be a good idea to try replacing it anyway, especially if the component is quite old. Once you have done this, you can reset the DTCs to see whether this error reappears.
• Inspect the hoses for cracks holes or signs of deformation, and install new parts if required. Replace any broken seals. Some holes or leaks may not be visible and will require a more advanced method of detection. They can often be detected using a smoke machine.
• You can test the purge flow solenoid for technical faults with a multimeter. The resistance value should usually be somewhere between 22.0 ohms and 30.0 ohms. Sometimes vent control solenoid or purge valve leaks can be detected with a simple blow test.