Keyoff Monitor

5 hours after the ignition switch is turned OFF, the electric leak detection 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 ignition 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 ignition switch is turned off, the monitor check starts 2.5 hours later.

Seque nce

Operation

Descriptions

Duration

-

ECM activation

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

-

Seque nce

Operation

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 70 kPa and 110 kPa (525 mmHg and 825 mmHg), ECM cancels EVAP system monitor.

10 seconds

B

First 0.02 inch leak criterion measurement

In order to determine 0.02 inch leak criterion, 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 they 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 normal.

10 seconds

E

Second 0.02 inch leak criterion measurement

After second 0.02 inch leak criterion measurement, leak check performed by comparing first and second 0.02 inch leak criterion.

If stabilized system pressure higher than second 0.02 inch leak criterion, 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:

0.02 Inch Leak Criterion Measurement

Canister Pressure Sensor

Fuel Tank

Vent Valve: OFF (vent) Canister Pump Module

Canister Filter

Leak Detection Pump: OFF

OFF

^ M

fr ON^

r r^ i ! -b

Operation C: EVAP System Pressure Measurement

ON (closed)

Reference Orifice (0.02 Inch)

Operation D: Purge VSV Monitor

ON (closed)

s

N

n

Atmospheric Pressure

Negative Pressure

V

y

ON (closed)

A112612E02

1. Purge VSV stuck open

In operation C, the leak detection pump creates negative pressure (vacuum) in the EVAP (Evaporative Emission) 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 0.02 inch leak criterion x 0.2], 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).

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