Monitor Description

5 hours after the ignition switch is turned to 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.

Sequence

Operations

Descriptions

Duration

-

ECM activation

Activated by soak timer, 5 hours (7 or 9.5 hours) after ignition switch turned to 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 criterion (reference pressure) 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 (reference pressure) 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

Canister Pressure Sensor

Vent Valve: OFF (vent) Canister Pump Module

Canister Filter

Leak Detection Pump: OFF

Vent Valve: OFF (vent) Canister Pump Module

Canister Filter

Leak Detection Pump: OFF

OFF (vent)

Reference Orifice (0.02 Inch)

OFF (vent)

Operation C: EVAP System Pressure Measurement

Reference Orifice (0.02 Inch)

Operation D: Purge VSV Monitor y

ON (closed)

□ Atmospheric Pressure

Negative Pressure

ON [f

-1-

ON (closed)

1. P0455: EVAP (Evaporative Emission) gross leak

In operation C, the leak detection pump creates negative pressure (vacuum) in the EVAP system and the EVAP system pressure is measured. If the stabilized system pressure is higher than [second 0.02 inch leak criterion x 0.2] (near atmospheric pressure), the ECM determines that the EVAP system has a large leakage, illuminates the MIL and sets the DTC (2 trip detection logic).

2. P0456: EVAP very small leak

In operation C, the leak detection pump creates negative pressure (vacuum) in the EVAP system and the EVAP system pressure is measured. If the stabilized system pressure is higher than second 0.02 inch leak criterion, the ECM determines that the EVAP system has a small leakage, illuminates the MIL and sets the DTC (2 trip detection logic).

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