DTC P0446. Chevrolet Prizm 2001

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2001 🢒 Prizm 🢒 Engine 🢒 Engine Controls - 1.8L 🢒 DTC P0446

Circuit Description

The DTC P0446 Evaporative Emission (EVAP) Vent System Performance diagnostic monitors the operation of the EVAP canister vent solenoid and tests the EVAP system for leaks. The powertrain control module (PCM) monitors the positive or negative pressure in the fuel tank using the fuel tank pressure sensor. Under certain engine operating conditions, the PCM turns ON the EVAP pressure switching solenoid in order to monitor control pressure in the EVAP system. The PCM is able to detect any abnormal conditions by the fluctuation of this pressure. The diagnostics performed by the fuel tank pressure sensor can warn the driver of a malfunction in the EVAP system by illuminating the MIL. The EVAP control system prevents the emission of the fuel vapors. The fuel vapor generated in the fuel tank while driving or idling enters the EVAP canister where a charcoal element absorbs and stores the fuel vapor. The EVAP canister is purged by the PCM-controlled EVAP canister purge solenoid valve. The EVAP canister purge valve releases the fuel vapors into the intake manifold to be burned in the combustion process.

Conditions for Setting the DTC

•	The EVAP canister vent valve is OFF.

•	The pressure at the fuel tank pressure (FTP) sensor is not within the expected values.

OR:

•	The EVAP pressure switching solenoid is OFF.

•	The pressure at the fuel tank pressure sensor is not within the expected values.

OR:

The pressure indicated in the EVAP canister is equal to atmospheric pressure after the EVAP canister purge valve is turned OFF.

Action Taken When the DTC Sets

•	The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.

•	The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

Conditions for Clearing the MIL/DTC

•	The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.

•	A DTC will clear after 40 consecutive warm-up cycles have occurred without a fault.

•	A DTC can be cleared by using the scan tool Clear Information function.

Diagnostic Aids

•	If DTC P0446 is the only EVAP DTC set, the most likely cause is an inoperable EVAP pressure switching solenoid. Inspect the EVAP pressure switching solenoid carefully for faulty connections and erratic operation.

•	DTC P0446 is more likely to set during city driving. Avoid operating the vehicle on the highway when validating a DTC P0446.

•

An intermittent DTC P0446 can be caused by a faulty EVAP canister. An EVAP canister that has released carbon particles can cause the EVAP canister purge valve to fail and leak intermittently. Inspect the EVAP purge system for carbon contamination before returning the vehicle to service. Refer to Evaporative Emission System Cleaning .

•	For functional checks of the components listed above, refer to Evaporative Emission Control System Diagnosis .

•	If a DTC P0446 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section can verify whether the fault is present. Refer to Inspection/Maintenance Evaporative Emission System Set .

An intermittent malfunction may be caused by a fault in any of the EVAP solenoid electrical circuits. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .

If the DTC cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

Test Description

The numbers below refer to the step numbers in the diagnostic table.

The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

This step checks the EVAP control system components for correct installation or damage. Inspect all lines and hoses. This includes a manufacturer approved gas cap that is correctly installed and tightened.

This step determines if a FTP sensor malfunction is present. The input signal of the FTP sensor should indicate atmospheric pressure with the fuel tank filler cap removed. The FTP sensor will vary with atmospheric pressure. A typical pressure at sea level is between 0.0-0.99 mm Hg (0.0-0.5 in H2O).

This step checks for the correct function of the EVAP canister purge valve.

This step checks the control circuit of the EVAP canister purge valve. Because the control circuit of the EVAP canister purge valve is PWM, the test lamp flickers during illumination, when commanded ON by the scan tool. This is the normal condition, indicating that the PCM and control circuit are OK.

This step checks for a possible leak in the EVAP system. The purpose of this inspection is to determine whether 5 to 6 inches of H2O can be obtained and held for at least 2 minutes.

This step checks for leaks in the fuel supply system. By plugging the ORVR vent line and the EVAP vapor line, the fuel tank, the fuel filler hose assembly, and the fuel tank components can be pressurized and checked for leaks. Be sure to check all connections and sealing points for leaks.

This step checks whether there is trapped negative or positive pressure at the (FTP) sensor.

The EVAP canister has component parts that cannot be diagnosed or tested on the vehicle. The EVAP canister should be inspected off the vehicle and tested for correct operation by performing the EVAP canister inspection procedures in EVAP Control System Diagnosis.

This step determines if the malfunction that caused the DTC P0446 is still present. Operating the vehicle in Check mode enhances the diagnostic capabilities of the PCM. The EVAP diagnostic can be monitored on the scan tool under the I/M System Information. When the EVAP test displays a YES status, indicating that the purge system diagnostic is completed, check for DTC P0446 in the Last Test Failed screen of the scan tool. If there is no DTC P0446 displayed the EVAP system diagnostic has run and passed, indicating that no malfunction was present this time. The DTCs MUST be cleared in order to view the Current Status of the system diagnostics being performed. Do not forget that the I/M System Information tests only indicate that the test has run, not whether the test passed or failed. The Last Test Failed screen must be checked for related DTCs in order to determine the outcome of the diagnostic test involved.

Step

Action

Values

Yes

Schematic Reference: Engine Controls Schematics

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

Install a scan tool and check for DTCs.

Is a DTC P0450 or P0451 present?

Go to DTC P0450 or DTC P0451

Go to Step 3

Visually and physically inspect the EVAP control system for the correct installation and routing of the lines and hoses.

Refer to the Evaporative Emission Control System Description for EVAP system hose routing diagrams.

Visually and physically inspect all of the following components for cracks, leaks, or damage:

•	The EVAP canister purge valve

•	The fuel tank pressure (FTP) sensor

•	The EVAP pressure switching solenoid

•	The EVAP canister

•	The EVAP system lines, hoses, and fittings

•	The fuel tank

Inspect the fuel tank filler cap for the correct part and the correct installation.
Repair any faults found as necessary.

Was repair necessary?