EVAP - Fuel Vapour Evaporative Control System

Code P0446 refers to the EVAP system. Evaporative (Emission Control System Vent Control Circuit Malfunction).
There is a valve in this system that controls the flow of excess fuel vapour. The ECU, (the car's brain), is getting a bad signal from this valve. You'll need to get this sorted out soon as it will affect your fuel consumption and the emissions your vehicle produces.
The EVAP system keeps the parts in the fuel system as an airtight set up. This is to stop any fuel vapour escaping into the atmosphere by redirecting back through the engine.

DTC P0497: Evaporative Emission (EVAP) System No Flow During Purge
Circuit/System Description
The control module tests the evaporative emission (EVAP) system for a large leak, or a stuck closed EVAP canister purge valve. The control module monitors the fuel tank pressure (FTP) sensor signal to determine the EVAP system vacuum level. When the conditions for running are met, the control module commands the EVAP canister purge valve OPEN and the EVAP vent valve CLOSED. This allows engine vacuum to enter the EVAP system. At a calibrated time, or vacuum level, the control module commands the EVAP canister purge valve closed, sealing the system, and monitors the FTP sensor input in order to determine the EVAP system vacuum level. If the system is unable to achieve the calibrated vacuum level, or the vacuum level increases too slowly, a DTC sets.

Diagnostic Aids
• A loose, missing, or damaged fuel fill cap can cause this DTC to set.
• A stuck closed, blocked, or restricted EVAP canister purge solenoid valve, can cause this DTC to set.
• A blockage or restriction in the EVAP canister purge solenoid valve vacuum supply hose, EVAP canister purge solenoid valve purge pipe, EVAP canister, or vapor pipe, can cause this DTC to set.
• A temporary blockage in the EVAP canister purge solenoid valve, purge pipe or EVAP canister could cause an intermittent condition. Inspect and repair any restriction in the EVAP system.
• To help locate intermittent leaks, use the J 41413-200 Evaporative Emissions System Tester (EEST) to introduce smoke into the EVAP system. Move all EVAP components while observing smoke with the J 41413-SPT High Intensity White Light. Introducing smoke in 15 second intervals will allow less pressure into the EVAP system. When the system is less pressurized, the smoke will sometimes escape in a more condensed manner.
• To improve the visibility of the smoke exiting the EVAP system, observe the suspected leak area from different angles with the J 41413-SPT .
• Observe the Freeze Frame/Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition occurs that caused the DTC to set. This may assist in diagnosing the condition.

The purge solenoid valvend canister are part of the EVAP system. The automatic diagnostic method tests the integrity of the EVAP system for leaks by pressurizing everything and then checking to see if pressure is lost. The filler cap is the main seal to the gas tank and if this is loose then compromises the ability of the system to be pressurized. Put a film of grease around the rubber seal and fit the cap tightly.

The following is a brief overview of the system (any spelling anomalies are due to my British background). I hope you find it helpful :-

What is it? The EVAP system is a collection of pipes and devices designed to prevent fuel vapour emission to protect the environment.

Where is it located? Pipes run from the top of the fuel tank to the carbon (vapour trap) canister which can be located between the inner and outer fenders (wings), on the inner fender or on the firewall (bulkhead). A pipe connects the canister to the throttle: the pipe exits just in front of the throttle plate.

How does it work? The EVAP system passively stores the vapour from the fuel tank in a charcoal filled canister. When the engine is running above idle speed the ECU opens a purge valve to the pipe leading to the throttle body. A vent valve allows the ingress of air into the canister and this encourages fuel vapour to be drawn out through the purge valve to be added to the air intake mixture to be burnt. The opening of the purge valve cycles with engine speed. The purge valve should be closed during idle.

Symptoms of faulty EVAP

• Erratic idling - If the purge valve fails to close the ingress of unmetered air will compromise the ECU's ability to maintain a suitable air/fuel ratio.

How to check? Simply clamping off the pipe from the EVAP purge valve should result in an immediate improvement in engine idling performance. Remove the purge valve and try to blow through it. If there is resistance then the valve is mechanically OK. Applying voltage to the electrical connections should open the valve and remove any resistance to blowing.

How to fix? If the valve is jammed open permanently or fails to open when signaled to do so then replace it. It may be possible, taking the greatest of care in the process, to open the valve to clean it up in the hopes of affecting a repair. If the solenoid itself, however, shows 'open-circuit' due to an electrical break it is best to replace it.

The Diagnostic Trouble Code table says for P0441 Evap Ctrl System Incorrect Purge:

General Description

The evaporative emission control system prevents hydrocarbon (HC) vapors from the fuel tank from escaping into the atmosphere where they could form photochemical smog. Gasoline vapors are collected in the charcoal canister. The ECM controls the Purge Control Solenoid Valve (PCSV) to purge any collected vapors from the canister back to the engine for combustion. This valve is actuated by the purge control signal from the ECM and controls fuel vapor from the canister to the intake manifold.
DTC Description

During "test of vapour generation" a new value from the tank pressure sensor is measured and compared with the start pressure at beginning of "test of vapour generation".
The ECM sets DTC P0441 if the pressure signal decrease occurs and the difference is below the predetermined threshold. If same error code is set in the next driving cycle, the ECM illuminates the MIL.

Unfortunately, this is not the 'turn gas cap 3 clicks" fault. Your likely cause is the PCSV valve is sticking in the open position.

Your test inspection procedure is:

System Inspection
PCSV Inspection
1. Ignition "OFF" .
2. Disconnect the hose leading from the PCSV to the intake manifold at PCSV.
3. Using a vacuum pump, apply specified vacuum(Approx. 15 in, Hg) to the manifold side of the valve and verify PCSV holds vacuum.
4. Ignition "ON" & Engine "OFF".
5. Install scantool and select "EVAP PURGE VALVE" on the Actuation Test mode.
6. Activates "EVAP PURGE VALVE" by pressing "STRT(F1)" key.
7. Verify PCSV release vacuum while valve is activating(should hear a faint click from PCSV).
8. Repeat this procedure 4 or 5 times to ensure PCSV reliability.
9. Is PCSV working properly?
YES
? Thoroughly check fuel vapor hoses and hose clamp and replace as necessary. Go to "Terminal and connection inspection" procedure.
NO
? Thoroughly check fuel vapor hoses and hose clamps between PCSV and intake manifold. Repair as necessary.
If OK, test with a new PCSV and check for proper operation. If problem is corrected, replace PCSV and go to "Verification of Vehicle Repair" procedure

I realize you probably do not have a ScanTool, as this is a dealer testing console. You should start by inspecting the hoses and connection to the PCSV.

P0441 : Evap. Emission System Incorrect Purge Flow

General Description
The evaporative emission control system prevents hydrocarbon (HC) vapors from the fuel tank from escaping into the atmosphere where they could form photochemical smog. Gasoline vapors are collected in the charcoal canister. The ECM controls the Purge Control Solenoid Valve (PCSV) to purge any collected vapors from the canister back to the engine for combustlon. This valve is actuated by the purge control signal from the PCM and controls fuel vapor from the canister to the intake manifold.
Possible Cause : ● Leakage on hose to PCSV ● Defective PCSV