Charcoal canister (EVAP System)
Evaporative Emission Control System (DTC P0440, P0441, P442, P0446, P0450, P0451, etc)
Approximately 20%of all hydrocarbon (HC) emissions from the automobile originate from evaporative sources. The Evaporative Emission Control (EVAP) System is designed to store and dispose of fuel vapors normally created in the fuel system; thereby, preventing its escape to the atmosphere. The EVAP system delivers these vapors to the intake manifold to be burned with the normal air/fuel mixture. This fuel charge is added during periods of closed loop operation when the additional enrichment can be managed by the closed loop fuel control system. Improper operation of the EVAP system may cause rich driveability problems, as well as failure of the Two Speed Idle test or Enhanced I/M evaporative pressure or purge test.
The EVAP system is a fully closed system designed to maintain stable fuel tank pressures without allowing fuel vapors to escape to the atmosphere. Fuel vapor is normally created in the fuel tank as a result of evaporation. It is then transferred to the EVAP system charcoal canister when tank vapor pressures become excessive. When operating conditions can tolerate additional enrichment, these stored fuel vapors are purged into the intake manifold and added to the incoming air/fuel mixture.
The old EVAP control system is a system which utilizes the intake manifold vacuum to draw the evaporative emissions into the intake manifold and mix then in with the intake air. The ECM controls a duty–cycle type VSV (vacuum switching valve) to purge the evaporative emissions from the charcoal canister.
EVAP VSV Monitor (DTC P0441, im3) The ECM controls the opening and closing of the EVAP VSV (vacuum switching valve). When the EVAP VSV is opened, the engine speed and the air/fuel ratio should change. The ECM monitors both of the engine RPM and the air/fuel ratio for this EVAP system diagnostic test. If the ECM does not detect any change in the engine RPM or the air/fuel ratio when opening the EVAP VSV, the ECM will determine that there is a malfunction of the EVAP VSV and set a DTC.
The EVAP control system is a system which utilizes the intake manifold vacuum to draw the evaporative emissions into the intake manifold and mix them with intake air. The ECM controls a duty–cycle type VSV (vacuum switching valve) to purge evaporative emissions from the charcoal canister. The ECM uses the vapor pressure sensor to detect malfunctions in the evaporative emissions (EVAP) system. This diagnostic checks the function of the EVAP VSV and VSV for vapor pressure sensor, the integrity of these components and the fuel tank from the standpoint of fuel vapor emissions. When the VSV for vapor pressure sensor is closed, the ECM monitors the vapor pressure in the fuel tank. When it is open, the ECM monitors the vapor pressure in the charcoal canister. The ECM senses pressure in the fuel tank using the vapor pressure sensor. The ECM supplies the sensor with a regulated 5 V reference–voltage and the sensor returns a signal voltage between 0.5 V and 4.5 V according to the pressure level in the fuel tank. When the pressure in the fuel tank is low, the output voltage of the vapor pressure sensor is low. When it is high, the output voltage is high.
EVAP VSV Monitor (DTC P0441, im.4) In one part of this diagnostic, the ECM switches the EVAP VSV to apply manifold vacuum pressure to the EVAP system. The ECM then monitors the vapor pressure in the charcoal canister. It is normal for the vapor pressure decrease when the EVAP VSV is opened. If the ECM detects no reduction in vapor pressure it interprets this as a “stuck closed” malfunction in the EVAP VSV. In a second part of this diagnostic, the ECM checks the vapor pressure of the charcoal canister with the EVAP VSV off. If the vapor pressure of the canister remains low, the ECM interprets this as a “stuck open” malfunction in the EVAP VSV. In either case, the ECM will illuminate the MIL and set a DTC.
1996–2003 ADDITION OF OBD
For example, this Scion tC (a '06) Data by TechStream Lite Kit
NEW DTC of EVAP System (for Toyota/Lexus/Scion)
P043E Evaporative Emission System Leak Detection Reference Orifice Low Flow
P043F Evaporative Emission System Reference Orifice High Flow
P1420 Evaporative Emission
Canister Small Leak (LS600hL)
P1422 Fuel Tank Small Leak
P2024 Evaporative Emissions (EVAP)
Vapor Temperature Sensor Circuit
P2400 Evaporative Emission
System Leak Detection Pump Control Circuit / Open
... Evaporative Emission Leak Detection Pump Stuck ON LC ‘06
P2411 Fuel Cap Sensor/Switch Circuit High
P2412 Fuel Cap Sensor/Switch Circuit Intermittent/Erratic
2419 Evaporative Emission Pressure Switching Valve Stuck ON LC ‘06
P2419 Evaporative Emission System Switching Valve Control Circuit Low (LS600hL)
P2420 Evaporative Emission Pressure Switching Valve Stuck OFF LC ‘06