PRE-RELEASE
DTC P0446
| DTC P0446 |
| Diagnostic Instructions |
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Perform the
Diagnostic System Check - Vehicle
prior to using this diagnostic procedure.
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Review
Strategy Based Diagnosis
for an overview of the diagnostic approach.
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Diagnostic Procedure Instructions
provides an overview of each diagnostic category.
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| DTC Descriptor |
DTC P0446
Evaporative Emissions (EVAP) Vent System Performance
| Circuit/System Description |
This DTC tests the evaporative emission (EVAP) system for a restricted or blocked EVAP vent path that would cause excess amounts of vacuum to be developed in the EVAP system. With the purge valve open and the canister vent valve open, if the EVAP system vacuum goes above a calibrated threshold, the test will fail.
| Typical Scan Tool Data |
| Fuel Tank Pressure Sensor Signal Voltage | Fuel Tank Pressure |
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1.5 V
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Atmospheric Pressure/BARO
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Less than 1.5 V
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Positive Pressure
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More than 1.5 V
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Negative Pressure/Vacuum
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| Conditions for Running the DTC |
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Before the ECM can report DTC P0446 failed, DTCs P0450, P0451, P0452, and P0453 must run and pass.
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DTC P0100, P0101, P0102, P0103, P0111, P0112, P0113, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0128, P0221, P0222, P0223, P0443, P0449, P0451, P0452, P0453, P0458, P0459, P0496, P0497, P0498, P0499, P0560, P0562, P0563, P0700, P2122, P2123, P2127, P2128 or P2138 is not set.
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The ignition voltage is 10-18 volts.
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The Closed Loop fuel control is enabled.
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The engine run time is greater than 10 minutes or the fuel trim is stable.
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The engine is operating at idle.
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The Fuel Tank Pressure is between -18.7 and +9.8 mm Hg (-10.0 and +5.2 in. H2O).
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The ambient air temperature (AAT) is between 2-32°C (35-90°F).
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The ECT and the IAT are within 10°C (18°F) of each other at engine start-up.
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The barometric pressure (BARO) is greater than 68 kPa.
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The long term fuel trim remains steady, less than 3 percent change in 200 ms over a period of 8 seconds.
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The fuel level is between 11-88 percent.
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The vehicle speed sensor (VSS) is less than 3 km/h (2 mph).
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The above conditions exist for greater than 5 seconds.
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DTC P0446 will attempt to run up to 10 times or until the test completes successfully once per ignition cycle.
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| Conditions for Setting the DTC |
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The Fuel Tank Pressure Sensor is less than -7.5 mm Hg (-4.0 in. H2O).
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The condition is exists for greater than 4 seconds or a cumulative of 30 seconds.
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| Action Taken When the DTC Sets |
DTC P0446 is a Type B DTC.
| Conditions for Clearing the DTC |
DTC P0446 is a Type B DTC.
| Diagnostic Aids |
An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at the EVAP vent valve inlet or a pinched vent hose. A blockage in the vent system may also cause a poor fuel fill problem.
| Reference Information |
Schematic Reference
Engine Controls Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Evaporative Emission Control System Description
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
| Circuit/System Verification |
| 1. |
Ignition ON and fuel cap removed, verify that the Fuel Tank Pressure Sensor parameter is between 1.3-1.7 volts.
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If not within the specified range, go to the fuel tank pressure sensor section in Circuit/System Testing.
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Install the fuel cap.
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With the engine running, the EVAP canister vent solenoid valve open, use a scan tool to command the EVAP canister purge solenoid valve to 100 percent. The fuel tank vacuum should not increase to more than -15 mmHg (-8 inches H2O).
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If the fuel tank vacuum is greater than the specified range, go to the restriction section in Circuit/System Testing.
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Using the scan tool, decrease the canister purge duty cycle from 100 percent to 0 percent. The vacuum should decrease to near zero.
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If the fuel tank vacuum does not return to zero or appears to decrease too slowly go to the restriction section in Circuit/System Testing.
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Run the vehicle within the Conditions for Running the DTCs. You may also operate the vehicle within the conditions that you have noted from the Freeze Frame/Failure Records data.
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| Circuit/System Testing |
| Important | ||
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Perform the Circuit/System Verification before proceeding with the Circuit/System Testing. |
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Restriction
| 1. |
With the engine running, the EVAP canister vent solenoid valve open, and the EVAP canister purge solenoid valve commanded to 100 percent, the fuel tank vacuum should not increase to more than -15 mmHg (-8 inches H2O).
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| 2. |
If the fuel tank vacuum is greater than the specified value, isolate the restriction by disconnecting one component at a time while the EVAP canister purge solenoid valve is commanded to 100 percent and the vent valve is open.
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Using the scan tool, decrease the canister purge duty cycle from 100 percent to 0 percent. The vacuum should decrease to near zero.
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If the fuel tank vacuum does not return to zero, or appears to decrease too slowly, inspect the components in the EVAP vent system for a restriction.
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Fuel Tank Pressure
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Ignition OFF, disconnect the harness connector at the fuel tank pressure sensor.
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Ignition OFF, test for less than 5 ohms between the low reference circuit terminal and ground.
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If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the fuel tank pressure sensor.
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| Repair Instructions |
Evaporative Emission Canister Vent Solenoid Valve Replacement
| Repair Verification |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
With the engine running, the EVAP canister vent solenoid valve open and the EVAP canister purge solenoid valve commanded to 100 %, the fuel tank vacuum should not increase to more than -15 mmHg (-8 inches H2O).
