P0446
Circuit Description
The PCM tests the EVAP system for the following conditions:
^ Large and small leaks (P0440 and P0442)
^ Excess vacuum (P0446)
^ Purge flow during non-commanded conditions (P1441)
^ Fuel Pressure sensor and Fuel Level sensor faults (P0452, P0453, P0462 and P0463)
^ EVAP Purge and Vent Valve faults (P0443 and P0449)
The PCM monitors the amount of vacuum and the amount of pressure in the EVAP system by monitoring the Fuel Tank Pressure sensor. For this DTC the PCM turns ON both the EVAP Purge Valve and the EVAP Vent Valve when the Conditions for Running the DTC are met. This applies an engine vacuum to a closed EVAP system. The PCM turns OFF both the EVAP Purge Valve and the EVAP Vent Valve when the system reaches a correct amount of vacuum. The EVAP system should quickly RELEASE the vacuum in the EVAP system with the EVAP Purge Valve OFF and the EVAP Vent Valve OFF (open). This test indicates a blocked or restricted EVAP Vent Valve or path if the EVAP system fails to release the vacuum quickly enough. This DTC will set after two consecutive failures of the above test.
Conditions for Running the DTC
^ No misfire, fuel trim, injector control circuit, AIR, EGR, VSS, HO2S, TP, MAP, MAF, ECT or IAT DTCs set.
^ Battery voltage is between 5 and 18 volts.
^ Barometric pressure is more than 75 kPa.
^ Fuel level is between 15% and 85% of full capacity for at least 10 seconds continuously. The time limit is required because fuel sloshing within the tank may cause the fuel level indication to vary outside the fuel level limits.
^ ECT at start up was between 4°C and 30°C (40°F and 86°F).
^ IAT at start up was between 4°C and 30°C (40°F and 86°F).
^ ECT not more than 8°C above or 2°C below IAT at start up.
Conditions for Setting the DTC
^ The EVAP system exceeds a vacuum threshold.
OR
^ There is too much system vacuum present at the start of this test.
Important: This DTC does NOT report a first failed test. A first fail of this DTC will have a scan tool status as NOT Run. Use the scan tool data display parameter EVAP TEST RESULT to determine if this DTC has failed or passed for THIS ignition cycle.
Action Taken When the DTC Sets
Important: Although these diagnostics are considered type A, they act like type B diagnostics under certain conditions. Whenever the EVAP diagnostics report that the system has passed, or if the battery has been disconnected, the diagnostic must fail during two consecutive cold start trips before setting a DTC. The initial failure is not reported to the diagnostic executive or displayed on a scan tool. A passing system always reports to the diagnostic executive immediately.
^ The PCM will illuminate the MIL during the first trip in which the diagnostic test has been run and failed.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.
Conditions for Clearing the MIL/DTC
^ The PCM turns the MIL Off after three consecutive drive trips that the diagnostic runs and does not fail.
^ A last test failed (current DTC) clears when the diagnostic runs and does not fail.
^ A History DTC clears after forty consecutive warm-up cycles, if this or any Other emission related diagnostic does not report any failures.
^ Use a scan tool in order to clear the MIL/DTC.
^ Interrupting the PCM battery voltage may or may not clear DTCs. This practice is not recommended.
Diagnostic Aids
Notice: Use the Connector Test Adapter kit J 35616-A for any test that requires probing the following items:
^ The PCM harness connectors
^ The electrical center fuse/relay cavities
^ The component terminals
^ The component harness connector
Using this kit will prevent damage caused by the improper probing of connector terminals.
Important: An accurate indication of fuel level is required for the PCM to properly Pass or Fail this DTC. Always diagnose fuel level sensor DTC's before performing this DTC's diagnostic table. Always check for fuel level sensor DTC's stored as History.
Perform a physical inspection of the EVAP system. Check for the following conditions:
^ A loose, missing, defective, or incorrect fuel tank cap
^ Incorrectly routed or defective EVAP system vacuum and vapor lines
^ A stuck closed EVAP Vent Valve
^ A restricted or blocked EVAP system hose
^ A restricted or stuck closed fuel tank rollover valve
^ A malfunctioning or damaged vapor canister
Check for charcoal release from the vapor canister.
If the vehicle had a P1441 stored and set a P0446 while performing the Service Bay Test inspect the EVAP Solenoid Purge Valve for Flow During Non-Purge (leakage).
The vacuum and pressure in the EVAP system is measured in inches of H2O (water). Most gauges measure vacuum in inches of Hg (mercury) and pressure in psi (pounds per square inch). The following shows how the values compare:
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
4. If the vacuum stored in the EVAP system is quickly released then an intermittent system restriction or failure of the EVAP Vent Valve or the EVAP Fuel Tank Pressure Sensor may have occurred.
5. Checking the vapor canister and the EVAP Vent Valve for restriction.
9. An EVAP Pressure sensor that does not correctly respond to pressure (or vacuum) will cause this DTC to set.
The EVAP Pressure Sensor monitors a range from 7.5 in. H2O of pressure to -17.5 in. H2O of pressure (vacuum).
In order to test the EVAP Pressure sensor for pressure response SEAL the system with the scan tool and use the EVAP pressure/purge diagnostic cart to apply pressure to the system. Compare the pressure gauge (in. H2O) on the diagnostic cart to the EVAP Pressure sensor reading on the scan tool.