Timing Chart

Total OBD & ECU Auto Diagnostics

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Order

Operation

Description

Time

Pressure

Measurement

The ECM turns the vent valve OFF (vent) and measures EVAP system pressure to memorize the atmospheric pressure.

Pressure

Measurement

The leak detection pump creates negative pressure (vacuum) through a 0.02 in. orifice and the pressure is measured. The ECM determines this as the 0.02 in. leak pressure.

20 sec.

3)

EVAP Leak Check

The leak detection pump creates negative pressure (vacuum) in the EVAP system and the EVAP system pressure is measured. If the stabilized pressure is larger than the 0.02 in. leak pressure, ECM determines that the EVAP system has a leak.

If the EVAP pressure does not stabilize within 15 minutes, the ECM cancels EVAP monitor.

Within 15 min.

4)

Purge VSV Monitor

The ECM opens the purge VSV and measures the EVAP pressure increase. If the increase is large, the ECM interprets this as normal.

10 sec.

5)

Repeat 0.02 in. Leak Pressure Measurement

The leak detection pump creates negative pressure (vacuum) through the 0.02 in. orifice and the pressure is measured. The ECM determines this as the 0.02 in. leak pressure.

20 sec.

6)

Final Check

The ECM measures the atmospheric pressure and records the monitor result.

b. Atmospheric Pressure Measurement

1) When the ignition switch is turned OFF, the purge VSV and the vent valve are turned OFF. Therefore, atmospheric pressure is introduced into the canister.

2) The ECM measures the atmospheric pressure based on the signals provided by the canister pressure sensor.

3) If the measurement value is out of standards, the ECM actuates the leak detection pump in order to monitor the changes in the pressure.

D13N22

c. 0.02 in. Leak Pressure Measurement

1) The vent valve remains off, and the ECM introduces atmospheric pressure into the canister and actuates the leak detection pump in order to create a negative pressure.

2) At this time, the pressure will not decrease beyond a 0.02 in. pressure due to the atmospheric pressure that enters through a 0.02 in. diameter reference orifice.

3) The ECM compares the logic value and this pressure, and stores it as a 0.02 in. leak pressure in its memory.

4) If the measurement value is below the standard, the ECM will determine that the reference orifice is clogged and store DTC (Diagnostic Trouble Code) P043E in its memory.

5) If the measurement value is above the standard, the ECM will determine that a high flow rate pressure is passing through the reference orifice and store DTC (Diagnostic Trouble Code) P043F, P2401 and P2402 in its memory.

P2401 Toyota Corolla

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