If the engine coolant temperature is not below C F hours after the ignition switch is turned OFF the monitor check starts hours later If it is still not below C F hours after the ignition switch is turned OFF the monitor check starts hours later

Sequ ence

Operations

Descriptions

Duration

-

ECM activation

Activated by soak timer 5, 7 or 9.5 hours after ignition switch turned OFF.

-

Sequ ence

Operations

Descriptions

Duration

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 76 kPa-a and 110 kPa-a (570 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*

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

F

Final check

Atmospheric pressure measured and then monitoring result recorded by ECM.

-

*: If only a small amount of fuel is in the fuel tank, it takes longer for the EVAP pressure to stabilize.

Operation A: Atmospheric Pressure Measurement

Purge VSV: OFF,

Operation B, E:

Reference Pressure Measurement

Canister Pressure Sensor

Fuel Tank

Vent Valve: OFF (vent) Canister Pump Module

Canister Filter

Leak Detection Pump: OFF

OFF (vent)

Operation C: EVAP System Pressure Measurement

ON (closed)

Reference Orifice (0.02 Inch)

Operation D: Purge VSV Monitor

ON (closed)

c

\

Atmospheric Pressure

Negative Pressure

V

J

ON (closed)

A112612E01

(a) P043E: Reference orifice clogged

In operation B, the leak detection pump creates negative pressure (vacuum) through the reference orifice. The EVAP system pressure is then measured by the ECM, using the canister pressure sensor, to determine the reference pressure. If the pressure is lower than -4.85 kPa-g (-36.4 mmHg-g), the ECM interprets this as a clog malfunction in the reference orifice, and stops the EVAP system monitor. The ECM then illuminates the MIL and sets the DTC (2 trip detection logic).

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