Engine off natural vacuum leakage check for onboard diagnostics

A diagnostic method for detecting leaks in a vapor handling system of a vehicle, comprising:

• sensing pressure and vacuum in a fuel tank of said vehicle;
• recovering vapor from said fuel tank using a canister;
• selectively providing atmospheric air to said canister using a canister vent;
• executing a leakage detection test using a controller, wherein said leakage detection test detects leaks in said vapor handling system that have a minimum diameter on the order of 0.020 inch;
• and
• generating data sets having greater than 25 standard deviations between leakage and no-leakage data sets.

A diagnostic system for detecting leaks in a vapor handling system of a vehicle, comprising:

• a fuel tank;
• a pressure/vacuum sensor that senses pressure and vacuum in said fuel tank;
• a canister for recovering vapor from said fuel tank;
• a canister vent solenoid for selectively providing atmospheric air to said canister;
• a controller connected to said canister vent solenoid and said pressure/vacuum sensor that executes a leakage detection test that detects leaks in said vapor handling system;
• wherein said leakage detection test includes a volatility test phase;
• wherein said volatility test phase classifies a volatility of said vapor in said fuel tank;
• wherein said leakage diagnostic test is aborted if said volatility is high;
• wherein said leakage diagnostic test includes a pressure phase that is performed after said volatility test phase;
• wherein, during said pressure phase, said controller closes said canister vent solenoid and measures a pressure change in said fuel tank;
• wherein, during said pressure phase, if said pressure is increasing and said pressure change exceeds a pressure target value, said controller initiates an analysis phase;
• and
• wherein, during said pressure phase, if said pressure is not increasing, said controller checks for a vacuum and performs a vacuum phase if said vacuum is present.

A diagnostic method for detecting leaks in a vapor handling system of a vehicle comprising:

• sensing pressure and vacuum in a fuel tank of said vehicle;
• recovering vapor from said fuel tank using a canister;
• selectively providing atmospheric air to said canister using a canister vent;
• and
• executing a leakage detection test using a controller, wherein said leakage detection test detects leaks in said vapor handling system;
• performing a volatility test phase during said leakage detection test;
• classifying a volatility of said vapor m said fuel tank during said volatility test;
• wherein said leakage diagnostic test is aborted if said volatility is high;
• wherein said leakage diagnostic test includes a pressure phase that is performed after said volatility test phase;
• measuring a pressure change in said fuel tank during said pressure phase;
• and
• initiating an analysis phase during said pressure phase if said pressure is increasing and said pressure change exceeds a pressure target value.