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. If a sufficient vacuum pressure level cannot be achieved, a large leak fault is detected.

The following are possible conditions that can result in a large leak detection:

• Missing, loose or faulty fuel cap.
• Poor electrical connections or faulty fuel tank pressure sensor.
• Disconnected or damaged EVAP vent hose.
• Disconnected, damaged, pinched or blocked fuel tank vapor lines.
• Poor connections or faulty EVAP canister purge valve or vent solenoid.
• Open ignition feed to either vent or purge solenoids.
• Damaged or leaking EVAP canister.
• Leaking fuel sender assembly or "O" ring, or leaking fuel tank or filler neck

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 are 14-122°F (-10 to 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.
• Abort time is 600 seconds and 240 seconds to finish once started.
• Vacuum threshold of 8 in. H2O not achieved.