Circuit Description

Once every drive cycle, the EVAP system runs a 25-40 second diagnostic where it monitors possible leaks, fuel tank pressure sensor, vent valve and canister purge valve. This diagnostic has 5 phases and can set several DTCs depending on which part of the diagnostic it fails. This DTC can set in the 2nd phase if tank pressure falls while vent and purge valves are both commanded shut. It will also set in the 4th phase if pressure falls to less than a calibrated value too quickly. This DTC indicates that purge valve is stuck open.

DTC will also set when:

• Vehicle speed is zero MPH.
• Engine at idle.
• Fuel system in closed loop.
• Battery voltage greater than 11.05 volts.
• Engine run time greater than 1.45 minutes.
• Altitude less than 9000 feet.
• Fuel level between 1.8-14 gallons.
• No TP, ECT, VSS, tank pressure, O2, idle control, purge valve, vent valve, battery voltage, misfire or EGR-related DTCs set.