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how do i fix trouble code p0446- evaporative emission ...

Customer Question

how do i fix trouble code p0446- evaporative emission control system vent control circuit malfunction. can I do this on my own?
Submitted: 8 years ago.
Category: Ford
Expert:  FORDFXR replied 8 years ago.


p0446indicates that self test has detected the evap systemhas excesive vacuum or vent control malfunction

possible causes are blockd or kinked hoses

contaminated canister

restricted canister

purge valve stuck

filler cap not venting

vref open to ftp sensor

damaged ftp sensor

Customer: replied 8 years ago.
Don't know what other info to give. Took my truck to the DEQ to have emissions test but it failed with the p0446 code and a p0153-02 sensor circuit slow response (Bank 2 sensor 1). Just wanting to know what I can do to fix this on my own. Don't have the money to take and have fixed right now but need to get it passed at the DEQ.
Expert:  FORDFXR replied 8 years ago.

it sounds to me that you have two separate issues, i donnot believe there is any way to tests for the first issue without some sort of scanner,


    • EVAP canister purge outlet tube (EVAP canister purge valve to EVAP canister) blockages or kinks.
    • EVAP canister tube (fuel tank to EVAP canister) blockages or kinks.
    • Fuel vapor elbow on EVAP canister contaminated.
    • Restricted EVAP canister.
    • Canister vent (CV) solenoid stuck closed (partially or fully).
    • Plugged or contaminated CV solenoid filter.
    • EVAP canister purge valve stuck open.
    • Fuel filler cap stuck closed (no vacuum relief).
    • VREF circuit open in fuel tank pressure (FTP) sensor.
    • Damaged FTP sensor.
  • Continuous Memory Diagnostic Trouble Code (DTC) P0446 or P1450 indicates that Self-Test has detected the Evaporative Emission Control System has excessive fuel tank vacuum. Also, a DTC P0446 indicates a vent control malfunction.

    Possible causes:

    Note: If the EVAP canister-CV solenoid and fuel tank assemblies are not accessible to perform the following step, GO to the Powertrain/Engine Group, Evaporative Emissions Section in the Workshop Manual for removal procedures.

  • Check for kinks or bends in the fuel vapor hoses/tubes (EVAP canister purge outlet tube and EVAP canister tube).
  • Visually inspect EVAP canister inlet port, CV solenoid filter and canister vent hose assembly for contamination or debris.
  • Check CV solenoid filter for blockage or contamination.
Is a fault indicated?
Yes No
REMOVE any contamination or debris around fuel vapor hoses/tubes and EVAP canister- CV solenoid assembly. REMOVE kinks or bends in EVAP canister purge outlet tube, EVAP canister tube and canister vent hose assembly. GO to HX19 . GO to HX19 .


  • Disconnect and plug the EVAP return tube (EVAP canister purge valve to intake manifold) at the intake manifold vacuum source.
  • Plug (tape) the CV solenoid (or filter) or plug the canister vent hose assembly.
  • Locate evaporative test port [marked EVAPORATIVE SERVICE PORT DO NOT USE UNREGULATED PRESSURE ABOVE 6.89 kPa (1 PSI)] near EVAP canister purge valve or EVAP canister.
  • Install Rotunda Evaporative Emission System Leak Tester 310-F007 (134-00056) or equivalent at the test port.
  • Regulate the nitrogen or argon gas pressure on the tester to 3.48 kPa (14 in-H2O).
  • Pressurize the EVAP system to 3.48 kPa (14 in-H2O).
  • Remove the plug (tape) from the CV solenoid or the plug from the canister vent hose assembly.
Does the EVAP system pressure drop rapidly (quickly)?
Yes No
REMOVE EVAP System Leak Tester from evaporative test port. REINSTALL evaporative test port cap. GO to HX20 . GO to Powertrain/Engine Group, Evaporative Emissions Section in the Workshop Manual for diagnostic symptom condition listed as Hiss When Opening Fuel Cap. REPEAT Pinpoint Test Step HX19 to VERIFY blockage no longer exists. GO to HX22 .


the second issure is on dealing with the engeine


  • Key on, engine running and engine at operating temperature.
  • Activate Key On, Engine Running (KOER) Self-Test.

Are DTCs P1127, P1128 or P1129 present during KOER Self-Test?

Yes No
GO to Section 4A, Powertrain Diagnostic Trouble Codes (DTC) Charts and SERVICE DTCs P1127, P1128 or P1129. GO to H21 .


    • DTC P0133 = HO2S-11
    • DTC P0153 = HO2S-21
    • Contaminated HO2S.
    • Exhaust leaks.
    • Shorted/open wires.
    • Improper fueling.
    • MAF sensor.
    • Deteriorating HO2S.
    • Air leaks.
  • Diagnostic Trouble Codes (DTCs) P0133 and P0153 indicate the response rate of the upstream HO2S(s) is below some calibrated window. The test measures the HO2S amplitude and output frequency. This is accomplished by superimposing a 1.5 to 2.5 Hz square wave over Lambse. The HO2S switching is monitored during this time to see if the calibration limit is met.

    DTC/HO2S Reference List:

    Possible causes:

  • Key off.
  • Scan Tool connected.
  • Key on, engine off.
  • Select Generic OBD II Function from the menu and trigger.
  • Press Continue.
  • Select Diagnostic Monitoring Test Results from the menu and trigger.
  • Scroll to Test ID: 01 trigger and press start.

Does the measured value indicate greater than 614?

Yes No
COMPLETE PCM Reset to clear DTCs. COMPLETE an HO2S Monitor Drive Cycle (REFER to Section 2A, Drive Cycles ). REPEAT Test Step H20 . If test results indicate a pass, testing is complete. Oxygen Sensor test results indicate a fail. GO to H22 .


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