Circuit Description

Evaporative (EVAP) emission system is checked by applying vacuum to the 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 the entire evaporative emission system. After the desired vacuum level has been achieved, EVAP canister purge valve is turned off, sealing the EVAP system. If a small leak is detected, DTC P0442 will be set under the following conditions.

Conditions required to set DTC are:

• No MAP, TPS, IAT, ECT, EGR, EVAP, VSS or system voltage DTCs set.
• BARO is greater than 72.3 kPa.
• Start-up IAT and ECT are 38-90°F (3.5-32.5°C).
• Difference between ECT and IAT at start up is less than 12.2°F (6.75°C).
• Vehicle speed is less than 60 MPH.
• Fuel tank level sensor reads 10-90 percent.
• Fuel level counts vary by less than 8 counts in .125 second time frame.
• Maximum engine run time is at least 540 seconds (9 minutes).
• Difference between the actual fuel tank pressure and the expected fuel tank pressure is less than the PCM's expectations.

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

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