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EVAP Control System Diagnosis (3.1L, 3.4L & 3.8L)

  1. Check for disconnected vacuum or purge lines, or a loose or missing fuel filler cap. Install scan tool. Turn ignition on, with engine off. Retrieve DTCs. If no DTCs are set, go to next step. If any DTCs are set, perform appropriate DTC test. See appropriate SELF-DIAGNOSTICS article.
  2. Turn ignition off. Disconnect canister purge line from EVAP canister purge valve. Turn ignition on, with engine off. Using scan tool, observe fuel tank pressure. If fuel tank pressure is zero in. H2 O, go to next step. If fuel tank pressure is not zero in. H2 O, go to step  9.
  3. Turn ignition off. Reconnect canister purge line to EVAP canister purge valve. Install EVAP Pressure/Purge Diagnostic Station (J-41413) to EVAP service port and zero gauges. Turn ignition on, with engine off. Using scan tool, command EVAP canister vent solenoid on. Using diagnostic station, pressurize EVAP system to 5 in. H2 O while observing fuel tank pressure on scan tool. If fuel tank pressure is 5 in. H2 O, go to next step. If fuel tank pressure is not 5 in. H2 O, perform DTC P0440 test. See appropriate SELF-DIAGNOSTICS article.
  4. Monitor EVAP pressure gauge on diagnostic station while maintaining fuel tank pressure at 5 in. H2 O. Using scan tool, observe fuel tank pressure. If fuel tank pressure is 5 in. H2 O, go to next step. If fuel tank pressure is not 5 in. H2 O, go to step  10.
  5. Monitor EVAP pressure gauge on diagnostic station while commanding EVAP canister vent solenoid off using scan tool. If EVAP pressure gauge decreases to near -5 in. H2 O within 2 minutes, go to next step. If EVAP pressure gauge does not decrease to near -5 in. H2 O within 2 minutes, perform DTC P0446 test. See appropriate SELF-DIAGNOSTICS article.
  6. Connect the in. Hg gauge of diagnostic station to purge valve canister side. Turn ignition on, with engine off. Using scan tool output test function, select SEAL SYSTEM and seal EVAP system. Start and idle engine. Increase engine speed to 1200-1500 RPM and observe vacuum gauge on diagnostic station. If vacuum increases to greater than zero in. Hg, go to next step. If vacuum does not increase to greater than zero in. Hg, go to step  11.
  7. Using scan tool, increase purge to 100 percent. Run engine at 1200-1500 RPM while monitoring vacuum gauge on diagnostic station. If vacuum increases to greater than 15 in. Hg, go to step  13. If vacuum does not increase to greater than 15 in. Hg, go to step  12.
  8. Turn ignition off. Disconnect EVAP canister line from fuel tank or EVAP canister. Turn ignition on, with engine off. Using scan tool, observe fuel tank pressure. If fuel tank pressure is zero in. H2 O, go to next step. If fuel tank pressure is not zero in. H2 O, perform DTC P0453 test. See appropriate SELF-DIAGNOSTICS article.
  9. Check for kinked or restricted canister purge line between EVAP canister purge valve and EVAP canister and repair as necessary. After repairs, go to step  13.
  10. Check for restricted fuel tank vapor line or EVAP purge line. If problem exists, repair as necessary and go to step  13. If problem does not exist, perform DTC P0452 test. See appropriate SELF-DIAGNOSTICS article.
  11. Check for no source vacuum to EVAP purge valve. After repairs, go to step  13.
  12. Check for carbon release into EVAP system. Locate and repair cause of no source vacuum to EVAP purge valve. If problem exists, repair as necessary and go to step  13. If problem does not exist, go to step  11.
  13. Reconnect all previously disconnected EVAP components. Turn ignition on, with engine off. Using scan tool output test function, select SEAL SYSTEM and seal EVAP system. Using diagnostic station, apply 15 in. H2 O pressure to EVAP system. If EVAP pressure gauge does not decrease to 10 in. H2 O within 2 minutes, system is okay. If EVAP pressure gauge decreases to 10 in. H2 O within 2 minutes, perform DTC P0446 test. See appropriate SELF-DIAGNOSTICS article.
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