Possible Causes
Fuel Filler Cap Not Properly inserted or Not Completely Tightened
Faulty Evaporative Emission System Switching Valve
Evaporative Emission System Switching Valve harness is open or shorted
Evaporative Emission System Switching Valve circuit poor electrical connection
Faulty Engine Control Module (ECM)
الأسباب المحتملة
Possible Symptoms
Engine Light ON (or Service Engine Soon Warning Light)
الأعراض المحتملة
Description
This fault code is stored in the Engine Control Module (ECM) when there is a malfunction with the Evaporative Emissions (EVAP) control circuit. The EVAP system allows the fuel tank to be vented in a controlled manner without releasing harmful gas emissions into the atmosphere. This is achieved by periodically allowing hydrocarbon emissions from the fuel tank into the intake manifold and enter the combustion process. The ECM monitors the circuit integrity by monitoring the inductive spike generated when the solenoid valve is switched off. This is caused by the collapse of the magnetic field resulting in a back EMF (electro-motive force). A solenoid normally has a resistance of 15 Ohms. The solenoid valve will be actuated by a pulse width modulated control via the engine control module. The solenoid can be powered up by a constant supply at system voltage or have a constant ground.
The system may not purge the carbon canister under idle conditions. The vehicle may need to be driven for the system to operate, an actuator test may be used to operate the solenoid valve with a scan tool.
Due to the presence of harmful hydrocarbons within the system manufacturers have to closely monitor the system, in some markets. This is achieved by the addition of certain hardware to measure system pressure and gas flow. The engine control module can monitor the system for leaks (both large and small) and for excessive or insufficient flow. This allows the technician access to more information relating to the fault and provides a better chance of an accurate diagnosis.
