2001 Buick Century

JETTE

MEMBER
2001 BUICK CENTURY
6 CYL
2WD
AUTOMATIC
89,000 MILES

Trouble code po446 I was told to replace the gas cap and did so / reset code to clear and after 2 days the service engine light comes back with the same code po446 evaporative emission control systems vent control circut malfunction what do I need to replace/ this is the second time I asked this question didnt get a responce yet?

1 Reply

BMRFIXIT

EXPERT

DTC P0446: EVAP CANISTER VENT BLOCKED

Circuit Description
This DTC tests EVAP system for a restricted or blocked EVAP vent path. PCM commands EVAP canister purge valve on and EVAP canister vent valve on. This allows a vacuum to be applied to EVAP system. Once a calibrated vacuum level has been reached, PCM commands EVAP canister purge valve off and EVAP canister vent valve off. PCM monitors Fuel Tank Pressure (FTP) sensor for a decrease in vacuum. If vacuum does not decrease to near zero inches H2O in a calibrated time, this DTC P0446 will set.

Code Enable Criteria
PCM will run diagnostic for this DTC under the following conditions:

� � � Ignition voltage is 10-18 volts.
� � � Barometric pressure is more than 75 kPa.
� � � Fuel level is 15-85 percent.
� � � Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) are between 39-86 °F (4-30 °C).
� � � Start-up ECT and IAT are 16 °F of each other.
� � � Vehicle speed is less than 75 MPH.
DTC will set when FTP is less than 10 in. H2O for at least 30 seconds.

Diagnostic Procedure

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
2. If DTC P0443, P0449, or P0453 are set, diagnose affected DTC first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS. If DTC P0443, P0449, or P0453 are not set, go to next
step.
3. Inspect EVAP vent valve for damage. Check for pinched EVAP vent hose. For component locations, see VACUUM DIAGRAMS - CARS article. If a problem is found, repair as necessary, then go to step 14. If no problems were found, go to next step. 4. Disconnect purge line from EVAP canister purge valve. Turn ignition on. Using scan tool, observe Fuel Tank Pressure (FTP) parameter. If scan tool displays zero in. H2O, go to next step. If scan tool does not display zero in. H2O, go to step 8.

NOTE: To avoid incorrect test results, do not pressurize EVAP system with more than 5 in. H2O.

5. Turn ignition off. Reconnect all previously disconnected components. Install Fuel Fill Cap Adapter (J 41415). Connect EVAP Pressure and Purge Station (J 41413) and fuel fill cap to fuel fill cap adapter. Turn ignition on. Using scan tool, command EVAP canister vent valve on. Using EVAP pressure and purge station, pressurize EVAP system to 5 in. H2O. Turn rotary switch on pressure and purge station to OFF/HOLD position. Using scan tool, command EVAP canister vent valve off. If scan tool indicates that FTP is about zero in. H2O, go to step 10. If scan tool does not indicate that FTP is about zero in. H2O, go to step 7.

6. Disconnect EVAP canister vent hose from EVAP canister vent valve. If scan tool indicates that FTP is -0.5 in. H2O to +0.5 in. H2O, go to step 10. If scan tool does not indicate that FTP is -0.5 in. H2O to +0.5 in. H2O, go to next step.

7. Disconnect EVAP vent pipe from EVAP canister. If scan tool indicates that FTP is about zero in. H2O, go to step 13. If scan tool does not indicate that FTP is about zero in. H2O, go to step 11.

8. Using scan tool, observe FTP sensor voltage. If scan tool displays more than 4.3 volts, see DTC P0453: FUEL TANK PRESSURE SENSOR CIRCUIT - HIGH VOLTAGE. If scan tool does
not display more than 4.3 volts, go to next step.

9. Inspect FTP sensor harness connector for poor connections. On Alero, Grand Am and Malibu, fuel tank must be removed for access to FTP sensor harness connector. On all other models, remove fuel sender access panel located under trunk liner. On all models, repair connector as necessary, then go to step 14. If connector is okay, go to step 12. 10. Replace EVAP canister vent valve. After repairs, go to step 14. 11. Replace EVAP canister. After repairs, go to step 14. 12. Replace FTP sensor. After repairs, go to step 14. 13. Repair blockage in EVAP vent hose. After repairs, go to next step. 14. Turn ignition on. Using scan tool, command EVAP canister vent valve on. Using EVAP pressure and purge station, pressurize EVAP system to 5 in. H2O. Turn rotary switch on pressure and purge station to OFF/HOLD position. Monitor pressure gauge on EVAP pressure and purge station. Using scan tool, command EVAP canister vent valve off. If pressure decreases, go to next step. If pressure does not decrease, go to step 3. 15. Using scan tool, observe all stored information. If scan tool displays any DTCs that have not been diagnosed, diagnose those DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS. If scan tool does not display any DTCs, system is okay.
Diagnostic Aids
An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at EVAP vent valve inlet or a pinched vent hose. A blockage in vent system will also cause a poor fuel fill problem.