Monitor Description

The two monitors, key-off and purge flow, are used to detect malfunctions relating to DTC P0441 The key-off monitor is initiated by the ECM internal timer, known as the soak timer, 5 hours* after the engine switch is turned off The purge flow monitor runs while the engine is running

1. KEY-OFF MONITOR

   5 hours* after the engine switch is turned off, the leak detection pump creates negative pressure (vacuum) in the EVAP system The ECM monitors for leaks and actuator malfunctions based on the EVAP pressure

   HINT

   * If the engine coolant temperature is not below 35°C (95°F) 5 hours after the engine switch is turned off, the monitor check starts 2 hours later If it is still not below 35°C (95°F) 7 hours after the engine switch is turned off, the monitor check starts 2 5 hours later

   SEQUENCE OPERATION CHART
   
   

   Sequence	Operation	Description	Duration
   -	ECM activation	Activated by soak timer 5, 7 or 9 5 hours after engine switch turned off	-
   A	Atmospheric pressure measurement	Vent valve turned OFF (vent) and EVAP system pressure measured by ECM in order to register atmospheric pressure If pressure in EVAP system not between 70 kPa-a and 110 kPa-a (525 mmHg-a and 825 mmHg-a), ECM cancels EVAP system monitor	10 seconds
   B	First reference pressure measurement	In order to determine reference pressure, leak detection pump creates negative pressure (vacuum) through reference orifice and then ECM checks if leak detection pump and vent valve operate normally	60 seconds
   C	EVAP system pressure measurement	Vent valve turned ON (closed) to shut EVAP system Negative pressure (vacuum) created in EVAP system, and EVAP system pressure then measured Write down measured value as it will be used in leak check If EVAP pressure does not stabilize within 15 minutes, ECM cancels EVAP system monitor	15 minutes(1)
   D	Purge VSV monitor	Purge VSV opened and then EVAP system pressure measured by ECM Large increase indicates normality	10 seconds
   E	Second reference pressure measurement	After second reference pressure measurement, leak check performed by comparing first and second reference pressure If stabilized system pressure higher than second reference pressure, ECM determines that EVAP system leaking	60 seconds
   -	Final check	Atmospheric pressure measured and then monitoring result recorded by ECM	-
   (1) If only a small amount of fuel is in the fuel tank, it takes longer for the EVAP pressure to stabilize.

   Fig 1: EVAP Pressure - Operation Diagram

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   1. Purge VSV stuck open

      In operation C, the leak detection pump creates negative pressure (vacuum) in the EVAP system. The EVAP system pressure is then measured by the ECM using the canister pressure sensor If the stabilized system pressure is higher than [second reference pressure x 0 32], the ECM interprets this as the purge VSV (Vacuum Switching Valve) being stuck open. The ECM illuminates the MIL and sets the DTC (2 trip detection logic)

      Fig 2: EVAP Pressure Reference Graph - When Purge Stuck Open

      Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   2. Purge VSV stuck closed

      In operation D, the canister pressure sensor measures the EVAP system pressure. The pressure measurement for the purge VSV monitor is begun when the purge VSV is turned ON (open) after the EVAP leak check. When the measured pressure indicates an increase of 0.3 kPa-g (2 25 mmHg-g) or more, the purge VSV is functioning normally. If the pressure does not increase, the ECM interprets this as the purge VSV being stuck closed. The ECM illuminates the MIL and sets the DTC (2 trip detection logic)

      Fig 3: EVAP Pressure Reference Graph (Purge VSV Stuck Closed)

      Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. PURGE FLOW MONITOR
   Fig 4: Purge Flow Monitor Chart

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   The purge flow monitor consists of the two step monitors. The 1st monitor is conducted every time and the 2nd monitor is activated if necessary

   • The 1st monitor

     While the engine is running and the purge VSV is ON (open), the ECM monitors the purge flow by measuring the EVAP pressure change. If negative pressure is not created, the ECM begins the 2nd monitor

   • The 2nd monitor

     The vent valve is turned ON (closed) and the EVAP pressure is then measured If the variation in the pressure is less than 0.3 kPa-g (2 25 mmHg-g), the ECM interprets this as the purge VSV being stuck closed, illuminates the MIL and sets DTC P0441 (2 trip detection logic)

Atmospheric pressure check.

In order to ensure reliable malfunction detection, the variation between the atmospheric pressures, before and after conduction of the purge flow monitor, is measured by the ECM.