Circuit Description

The EVAP system is tested with on-board diagnostics by applying pressure (vacuum) to the system and monitoring pressure change. PCM monitors vacuum level at fuel tank vapor pressure sensor. At appropriate time, the EVAP vent solenoid is commanded closed (normally open) and EVAP canister purge valve is commanded to a fixed duty cycle, allowing engine to draw vacuum on the entire evaporative emission system.

After a calibrated vacuum level is achieved, EVAP canister purge valve is turned off, sealing the system. A leak is detected by monitoring for a decrease in vacuum level over a calibrated period of time, while keeping all other variables constant.

Conditions for setting this DTC:

• DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0133, P0134 and P1144 are not set.
• BARO is greater than 80.8 kPa.
• Both ECT and IAT 14-122°F (10-50°C) at engine start-up.
• ECT and IAT are within 10 degrees of each other at start-up.
• Fuel tank level 15-85 percent.
• Engine run time is greater than 2 seconds.
• TP sensor between 9-35 percent.
• Vacuum decay slope is greater than a calibrated amount during test. Decay slope is proportional to fuel level.