P0446

Diagnostic Chart:

Wiring Diagram:

Circuit Description
The evaporative system includes the following components:

^ Fuel tank.
^ EVAP vent solenoid.
^ Fuel tank pressure sensor.
^ Fuel pipes and hoses.
^ Fuel vapor lines.
^ Fuel cap.
^ EVAP canister.
^ Purge lines.
^ EVAP canister purge valve.
^ EVAP service port.

The evaporative emission system is checked by applying vacuum to the EVAP system and 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 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 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 valve (EVAP vent solenoid Open, EVAP purge Pulse Width Modulation 0%) and monitoring the fuel tank vacuum sensor input. 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:

^ Faulty EVAP vent solenoid (stuck closed).
^ Plugged kinked or pinched vent hose.
^ Shorted EVAP vent solenoid driver circuit. Plugged evaporative canister.

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

Conditions for Setting the DTC

^ The Barometric pressure (BARO) is greater 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.
^ Intake Air Temperature is not more than 1°C (2°F) greater than the Engine Coolant Temperature at start up.
^ Engine Coolant Temperature is not more than 7°C (12°F) greater than the Intake Air Temperature at start up.
^ Fuel tank level is between 26% and 74%.
^ The Throttle Position (TP) sensor is between 9 and 35%.
^ The EVAP solenoid is at 50% Pulse Width Modulation (PWM) within 65 seconds of engine run time.
^ The EVAP system is unable to achieve or maintain vacuum during the diagnostic test. The amount of decay will vary with the fuel level.
^ DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118. P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134 and P1133 not set.

Action Taken When the DTC Sets

^ The Malfunction Indicator Lamp (MIL) will illuminate.
^ The PCM will record operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information.
^ A history DTC is stored.

Conditions for Clearing the MIL/DTC

^ The MIL will turn off after 3 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.
^ 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: Verity that the vent hose between the canister and the EVAP vent solenoid is not restricted.

Check for charcoal particles. Refer to Carbon Particle Removal from EVAP System before starting repairs. Service and Repair

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.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.

1. The Powertrain OBD 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. Repairing the electrical malfunction will very likely correct the condition that set DTC P0446.
4. Checks the fuel tank pressure sensor at ambient pressure.
6. Forces the fuel tank pressure sensor to re-zero.
7. Verifies that the fuel tank pressure sensor accurately reacts to EVAP system pressure changes.
9. Checks for a blocked EVAP canister.
13. Duplicates the Powertrain On-Board Diagnostic test.