P0446

DTC P0446 Evaporative Emission (EVAP) Vent System Performance




Circuit Description
The evaporative system includes the following components:
- The fuel tank
- The EVAP vent solenoid
- Fuel tank pressure sensor
- The fuel pipes and hoses
- The fuel vapor lines
- The fuel cap
- The EVAP canister
- The purge lines
- The EVAP canister purge solenoid valve
- The EVAP service port

The evaporative emission system is checked by applying vacuum to the EVAP system and by monitoring for a vacuum decay. The PCM monitors the vacuum level through the fuel tank pressure sensor signal. At an appropriate time, the EVAP canister purge solenoid valve and the EVAP 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 canister purge solenoid valve is turned OFF, sealing the system.

A restricted or blocked EVAP canister vent path is detected by drawing a vacuum on the EVAP system, turning OFF the EVAP vent solenoid and the EVAP canister purge solenoid valve (EVAP vent solenoid Open, EVAP purge PWM 0 percent) and monitoring the fuel tank vacuum sensor signal. With the EVAP 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:
- A malfunctioning EVAP vent solenoid (stuck closed)

- The vent hose for the following conditions:
- Plugged
- kinked
- Pinched

- A shorted EVAP vent solenoid driver circuit

- A plugged evaporative canister

If any of these conditions are present, DTC P0446 will set.

Conditions for Running the DTC
- No active MAP DTC's
- No active IAT DTC's
- No active ECT DTC's
- No active TP DTC's
- No active Oxygen Sensor DTC's
- No active Fuel Tank Pressure Sensor DTC's
- No active VSS DTC's
- No active PCM Memory DTC's
- The BARO is more than 75 kPa.
- The intake air temperature is between 5° C and 29° C (41° F and 84° F) at engine start up.
- The engine coolant temperature is between 5° C and 29° C (41° F and 84° F) at engine start up.
- The Intake Air Temperature is not more than 1° C (2° F) more than the Engine Coolant Temperature at start up.
- The Engine Coolant Temperature is not more than 7° C (12° F) more than the Intake Air Temperature at start up.
- The fuel tank level is between 15 percent and 85 percent.
- The TP sensor is between 7 percent and 35 percent.

Conditions for Setting the DTC
The EVAP system is unable to release vacuum during the diagnostic test.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The PCM will record the operating conditions at the time that the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information.
- The EVAP purge function is disabled until the diagnostic passes.
- A history DTC stores.

Conditions for Clearing the MIL/DTC
- The MIL will turn off after 3 consecutive ignition cycles in which the diagnostic runs a pass.
- A history DTC will clear after 40 consecutive warm up cycles without a malfunction.
- A scan tool can clear the DTCs.

Diagnostic Aids
Check for the following conditions:
- Poor connection at PCM: Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
- Damaged harness: Inspect the wiring harness to the EVAP vent solenoid and the fuel tank pressure sensor for an intermittent open or short circuit.
- Kinked, pinched or plugged vent hose: Verify that the vent hose between the canister and the EVAP vent solenoid is not restricted.

Check for charcoal particles. Refer to EVAP System Cleaning before starting repairs.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that causes the DTC to be set occurs. This may assist in diagnosing the condition.

Steps 1 - 4:

Steps 5 - 6:

Steps 7 - 10:

Steps 11 - 13:

Test Description
The numbers below refers to the step numbers on the Diagnostic Table.
1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.
3. If a vent solenoid electrical malfunction is present, the purge system will not operate correctly. Repairing the electrical malfunction will very likely correct the condition that set DTC P0446.
4. This step checks the fuel tank pressure sensor at the ambient pressure.
5. This step verifies that the fuel tank pressure sensor accurately reacts to the EVAP system pressure changes.
7. This step checks for a blocked EVAP canister.
11. This step duplicates the Powertrain On-Board Diagnostic test.