Circuit Description

Evaporative (EVAP) emission system is checked by applying vacuum to EVAP system and monitoring for a vacuum leak. PCM monitors vacuum level via fuel tank pressure sensor signal. When appropriate, EVAP canister purge valve and EVAP canister vent solenoid are turned on, allowing engine to draw a small vacuum on entire evaporative emission system. After desired vacuum level has been achieved, EVAP canister purge valve is turned off, sealing EVAP system. If a small leak is detected, DTC P0442 will be set.

Conditions required to set DTC are:

• BARO is greater than 72.3 kPa.
• No MAP, TPS, IAT, ECT, EGR, EVAP, VSS or system voltage DTCs set.
• Intake air and coolant temperatures are 40-95°F (4.2-35°C) at startup.
• Difference between ECT and IAT at start up is less than 12.2°F (6.75°C).
• Fuel level counts vary by less than 8 counts in .125 second time frame.
• On DTC P0442, fuel tank level sensor reads 15-85 percent.
• On DTC P0456, fuel tank level sensor reads 40-85 percent.
• Maximum engine run time is at least 390 seconds.
• Difference between actual fuel tank pressure and expected fuel tank pressure is less than PCM's expectation.

  The listed conditions are met, and following is met once:

• EVAP system is unable to maintain vacuum, depending upon amount of fuel in fuel tank, during diagnostic test.