P0446
P0446Evaporative Emission System Vent Control Circuit
Diagnostic conditions
- Battery voltage between 10 V and 16 V
- Engine must cool down by at least 42 °K in the time that elapses between stopping and restarting engine
- Intake air temperature between 5 °C and 95 °C
- Variations of intake air temperature less than 12 °K
- Vehicle is travelling with longer partial load share (3 - 150 km/h)
- Engine temperature higher than 5 °C
- Diagnosis only runs below 2400 m above sea-level
- No P0441, P0444, P0445 (EVAP canister purge valve) or P0446, P0447, P0448 (EVAP canister shutoff valve) faults in memory
- No P0455 tank system (major leak) fault in memory
- No P2400, P2401, P2402 (leakage diagnosis pump) fault in memory
- No P2403 and P2404 (reed switch) fault in memory
- Fuel tank leak test was started and completed (successfully or by abortion because time limit was exceeded, time since starting of engine between 11 and 20 minutes)
Possible cause of fault
- EVAP canister shutoff valve faulty (sticks in closed state or is blocked)
- Hose trapped or blocked, or air supply line in EVAP canister blocked
Affected terminals
-
Diagnosis/troubleshooting
NOTE:
- The fuel tank leak test for the Cayenne is carried out with approx. 20 mbar overpressure in the tank. This overpressure is built up by the leakage diagnosis pump and is evaluated using an integrated reed contact. The pump work is performed by a spring, which is stretched over a membrane by the vacuum from the intake manifold (or supply tank).
- The diagnostic conditions can also be 'forced' by performing the "Leakage Diagnosis" short test using the 9588 Porsche System Tester II.
- The EVAP canister shutoff valve actually acts as a by-pass to the leakage diagnosis pump. Once the leak test is complete, the pressure in the tank is reduced via the valve (and the open EVAP canister purge valve), thereby allowing the leakage diagnosis pump to revert to its initial setting. This opens the actual EVAP canister shutoff valve (this is mechanical and is integrated into the leakage diagnosis pump) and the EVAP canister is connected to the atmosphere again.
DANGER:
- If this fault is detected in a vehicle, it is possible that the fuel tank and ventilation system are under pressure.
- Therefore, before starting to work on the tank system, carefully release the overpressure by opening the tank cap slowly.
DANGER:
- Danger of toxication through petrol.
- Inhaling vapours can lead to irritation of the mucous membranes and eyes.
- It represents a serious risk to health when inhaled, touched or swallowed over longer periods.
- Wear a breathing mask with active charcoal filter; do not breathe in any fuel vapours.
- Wear protective gloves that are fuel-resistant.
- Only work on the fuel system in well-ventilated locations.
- Before opening fuel lines or fuel hoses, relieve the fuel pressure.
- Collect escaping fuel; absorb it if necessary with a suitable binding material and dispose of properly
- Pay attention to cleanliness when working on the fuel system.
DANGER:
- Risk of tire and explosion when handling petrol.
- Keep clear of ignition sources.
- Do not smoke.
- Do not carry out welding or grinding work in the immediate vicinity (naked flame and flying sparks).
- Prevent escaping fuel from coming into contact with hot engine components.
- Avoid electric discharges in the vicinity of escaped fuel.
- Secure the vehicle, e.g. with a warning sign.
- Change any clothing soaked with fuel immediately.
- In the event of a fire, use C02 or dry powder fire extinguishers.
Tank Diagnosis - EVAP Canister Shutoff Valve Blocked (Below Limit)
