P0446

DTC P0446: Evaporative Emission System Vent Control Malfunction

System Description
The evaporative (EVAP) emission system includes the following components:
- Fuel tank.
- EVAP emission vent solenoid.
- Fuel tank pressure sensor.
- Fuel pipes and hoses.
- Fuel vapor lines.
- Fuel cap
- EVAP emission canister.
- Purge lines.
- EVAP emission canister purge valve.
- EVAP emission service port.

The evaporative emission system is checked by applying vacuum to the EVAP emission system and monitoring for a vacuum decay. The engine control module (ECM) monitors the vacuum level through the fuel tank pressure sensor signal.
At the appropriate time, the EVAP emission canister purge valve and the EVAP emission vent solenoid are turned ON, allowing the engine to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, the EVAP emission canister purge valve is turned OFF, sealing the system.
A restricted or blocked EVAP emission canister vent path is detected by drawing a vacuum on the EVAP emission system, turning OFF the EVAP emission vent solenoid and the EVAP emission canister purge valve (EVAP emission vent solenoid Open, EVAP emission purge PWM 0%) and monitoring the fuel tank vacuum sensor input. With the EVAP emission vent solenoid open, any vacuum in the system should decrease quickly unless the vent path is blocked. A blockage can be caused by the following conditions:
- Faulty EVAP emission vent solenoid (stuck closed).
- Plugged kinked or pinched vent hose.
- Shorted EVAP emission vent solenoid driver circuit.
- Plugged evaporative canister.
- If any of these conditions are present, DTC P0446 will set.

Conditions for Setting the DTC
- DTC(s) P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0201, P0202, P0203, P0204, P0300, P0402, P0404, P0405, P0406, P0443, P0452, P0453, P0488, P0502, P0462, P0463, P0506, P0507, P2195, and P2196 will not set.

Common EVAP Enable Criteria
- System voltage is between 11V and 16V.
- Barometric Pressure (BARO) is greater than 72.3 kPa (10.5 psi).
- Engine soak time is greater than 720 minutes. Or, at startup IAT-ECT is less than 8�C (46.4�F).
- At start up, Engine coolant temperature (ECT) and Intake Air Temperature (IAT) are between 4�C (39.2�F) and 34�C (93.2�F).
- Startup IAT-IAT is less than 3�C (5.4�F).
- Purge enable time is less than pre-determined value based on startup ECT.
- Fuel level is between 6% and 93%.
- Engine run time is between 1 second and 360 seconds plus purge enable time.

Vent Blocked Enable Criteria
- Restricted path test time is less than 220 seconds.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.
- A history DTC is stored.

Conditions for Clearing the MIL/DTC
- The MIL will turn off after three consecutive ignition cycles in which the diagnostic runs without a fault.
- A history DTC will clear after 40 consecutive warm-up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.

Diagnostic Aids
Although this DTC is considered a type A diagnostic (refer to "Engine Control Module"), it acts like a type B diagnostic under certain conditions. Whenever this diagnostic reports the system has passed, or if the battery is disconnected, the diagnostic must fail twice 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.
Check for the following conditions:
1) Poor connection at ECM. Inspect harness connectors for the following conditions:
- Backed-out terminals
- Improper mating
- Broken locks
- Improperly formed
- Damaged terminals
- Poor terminal-to-wire connection

2) Damaged harness. Inspect the wiring harness to the EVAP emission vent solenoid and the fuel tank pressure sensor for an intermittent open or short circuit.

3) Kinked, pinched, or plugged vent hose. Verify that the vent hose between the canister and the EVAP emission vent solenoid is not restricted.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
(1) The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
(3) If a vent solenoid electrical malfunction is present, the purge system will not operate correctly.
(4) Checks the fuel tank pressure sensor at ambient pressure.
(5) Verifies that the fuel tank pressure sensor accurately reacts to EVAP system pressure changes.
(8) Checks for a blocked EVAP canister.
(11) Duplicates the OBD II diagnostic test.

Steps 1-6:

Steps 7-11:

Troubleshooting