Circuit Description

EVAP system includes fuel tank, fuel tank pressure sensor, EVAP pressure switching solenoid, fuel lines and hoses, vapor and purge lines, fuel cap, EVAP canister, and EVAP canister purge solenoid valve. Once every drive cycle, EVAP system will run a 25 to 40-second diagnostic where it monitors possible leaks at fuel tank pressure sensor, vent valve and canister purge valve.

This diagnostic has 5 phases and can set different DTC depending on which part of the diagnostic fails. If tank pressure is too slow reaching a certain value in the first phase, this DTC will set. If can also set in the third phase if tank pressure fails too slowly when vent and purge are both opened. This DTC indicates that a large leak is detected.

DTC will set when:

• Vehicle speed is zero MPH.
• Engine at idle.
• Fuel system in closed loop.
• ECT at start-up between 17-167°F (-8.25 to 75°C).
• IAT between 17-122°F (-8.25 to 50.3°C).
• Battery voltage greater than 11 volts.
• Engine run time greater than 1.45 minutes.
• Altitude less than 9000 feet.
• Fuel level between 1.85-14.0 gallons.
• No TP, ECT, VSS, fuel tank pressure, O2S, idle control, purge valve, vent valve, battery voltage, misfire and EGR DTCs set.

When DTC sets, MIL will illuminate after 2 consecutive ignition cycles in which diagnostic runs with active fault. ECM will record operating conditions at time of diagnostic failure and store information in freeze frame buffer.