P0446

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 powertrain control module(PCM)/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, P0121, P0122, P0123, P0131, P0132, P0133, P0134, P0137, P0138, P0140, P0141, P0201, P0202, P0203, P0204, P0300, P0402, P0404, P0405, P0406, P0449, P0452, P0453, P0506, P0507, P1130, P1133, P1134, P1171, P1404, P1627, and P1640 will not set.
- The system voltage is between 11 volts and 16 volts.
- Intake air temperature (IAT) is between 39 °F (4 °C) and 95 °F (35 °C) at engine start up.
- Engine Coolant Temperature (ECT) is between 39 °F (4 °C) and 95 °F (35 °C) at engine start up.
- Barometric Pressure (BARO) is greater than 72.3 kPa.
- At start-up, ECT-IAT is less than 46 °F (8 °C) or IAT/ECT is less than 54 °F (12 °C)
- Vehicle speed is less than 90 mph (145 kph).
- Fuel tank level is between 15% and 90%.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The PCM/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 "Powertrain Control Module/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 PCM/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.

Step 1 - 5:

Step 6 - 11:

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.