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Home >> Lexus >> 2008 >> IS 250 RWD, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 178 (Engine Control System (2GR-FSE) - DTC P0171 - P050A) >> DTC P0441 Evaporative Emission Control System Incorrect Purge Flow >> Monitor Description

Monitor Description

WARNING: This page is about a different car, the 2008 Lexus IS 350. However, it is still accessible from the selected car via links, so may be relevant.

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 electric vacuum pump creates negative pressure (vacuum) in the EVAP (Evaporative Emission) 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.

    OPERATION AND DESCRIPTION CHART

    Sequence Operation Description Duration
    - ECM activation Activated by soak timer, 5 hours (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 and 110 kPa (525 mmHg and 825 mmHg), ECM cancels EVAP system monitor.    		 10 seconds
    B First 0.02 inch leak pressure measurement In order to determine 0.02 inch leak pressure standard, vacuum pump creates negative pressure (vacuum) through 0.02 inch orifice and then ECM checks if vacuum 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 they will be used in leak check.
    If EVAP pressure does not stabilize within 15 minutes, ECM cancels EVAP system monitor.    		 15 seconds(1)
    D EVAP VSV monitor EVAP VSV opened and then EVAP system pressure measured by ECM.
    Large increase indicates normal.    		 10 seconds
    E Second 0.02 inch leak pressure measurement After second 0.02 inch leak pressure measurement, leak check performed by comparing first and second 0.02 inch leak pressure standards.
    If stabilized system pressure higher than second 0.02 inch leak pressure standard, ECM determines that EVAP system leaking.    		 60 seconds
    F Final check Atmospheric pressure measured and then monitoring result recorded by ECM. -
    HINT:
    (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 System Operation Diagram
    G05316044Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    1. EVAP VSV stuck open

      In operation C, the vacuum pump creates negative pressure (vacuum) in the EVAP (Evaporative Emission) system. The EVAP system pressure is then measured by the ECM using the pressure sensor. If the stabilized system pressure is higher than [second 0.02 inch leak pressure standard x 0.2], the ECM interprets this as the EVAP VSV (Vacuum Switching Valve) being stuck open. The ECM illuminates the MIL and sets the DTC (2 trip detection logic).

      Fig 2: EVAP System Pressure Chart - EVAP VSV Stuck Open
      G05822658Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
    2. EVAP VSV stuck closed

      In operation D, the pressure sensor measures the EVAP (Evaporative Emission) system pressure. The pressure measurement for EVAP VSV monitor is begun when the EVAP VSV is turned ON (open) after the EVAP leak check. When the measured pressure indicates an increase of 0.3 kPa (2.25 mmHg) or more, the EVAP VSV is functioning normally. If the pressure does not increase, the ECM interprets this as the EVAP VSV being stuck closed. The ECM illuminates the MIL and sets the DTC (2 trip detection logic).

    Fig 3: EVAP System Pressure Chart - EVAP VSV Stuck Closed
    G05822659Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  2. PURGE FLOW MONITOR 

    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 EVAP VSV (vacuum Switching Valve) 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 0.5 kPa (3.75 mmHg), the ECM interprets this as the EVAP VSV being stuck closed, and illuminates the MIL and sets DTC P0441 (2 trip detection logic).

    Fig 4: EVAP System Pressure Chart - Purge Flow Monitor
    G05200102Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

    Atmospheric pressure check:

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

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