Circuit Description

Evaporative leak detection strategy is based on applying vacuum to EVAP system and monitoring vacuum decay. Powertrain Control Module (PCM) monitors vacuum level by means of fuel tank vacuum sensor input. At a predetermined time, EVAP purge solenoid and EVAP vent solenoid are turned on. This allows engine vacuum to draw a small vacuum on entire EVAP system. After desired vacuum level has been achieved, EVAP purge solenoid is turned off, sealing the system. If a small leak is detected, a DTC P0442 will set.

Conditions for setting this DTC are as follows:

• DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134 and P1133 not set.
• BARO is greater than 75 kPa.
• ECT and IAT is 41-84°F (5-29°C) at engine start-up.
• IAT not greater than 2°F (1°C) of ECT at engine start-up.
• ECT not greater than 12°F (7°C) of IAT at engine start-up.
• Fuel tank level is 26-74 percent.
• TP angle is 9-35 percent.
• EVAP solenoid is enabled.
• EVAP system is unable to achieve or maintain vacuum during diagnostic test. Amount of vacuum decay will vary with fuel level.