DTC P0446 Evaporative Emission (EVAP) Vent System Performance. Chevrolet Prizm 1998

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1998 🢒 Prizm 🢒 DTC 🢒 DTC P0446 Evaporative Emission (EVAP) Vent System Performance

Engine Controls Components
Cell 20: EVAP Controls, IAC, PSP Switch
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The 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 the positive or negative pressure in different areas of 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 (cleaned) by the PCM controlled EVAP canister purge solenoid valve. The EVAP canister purge solenoid valve releases the fuel vapors into the intake manifold to be burned in the combustion process.

Conditions for Setting the DTC

•	The EVAP pressure switching solenoid is OFF.

•	The pressure in the EVAP canister is not within the expected values.

•	The EVAP pressure switching solenoid is ON.

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

The pressure indicated in the EVAP canister is equal to atmospheric pressure after purge cut off (EVAP canister purge solenoid valve is turned OFF).

Action Taken When the DTC Sets

•	The PCM illuminates the malfunction indicator lamp (MIL) after two 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 a 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.

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

The DTC P0446 daignostic checks for EVAP system leaks on the purge side of the EVAP system. A fault in any of the EVAP system components, except the fuel tank and filler pipe, can cause a DTC P0446 to set. Check for any of the following conditions:

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 solenoid valve to fail (leak) intermittently. Inspect the EVAP purge system for carbon contamination before returning the vehicle to service. Refer to Evaporative Emission System Cleaning .

•	A faulty fuel tank pressure sensor

•	A faulty EVAP canister purge solenoid valve

•	A faulty EVAP pressure switching solenoid

•	A faulty or leaking EVAP canister

•	Damaged or leaky hoses, lines, or fittings

•	A faulty or leaking fill limiter vent valve (FLVV)

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

An intermittent malfunction may be caused by a fault in any of the EVAP solenoid electrical circuits. Inspect the wiring harness and components for any of the following conditions:

•	Backed out terminals.

•	Improper mating of terminals.

•	Broken electrical connectors locks.

•	Improperly formed or damaged terminals

•	Faulty terminal to wire connections.

•	Physical damage to the wiring harness.

•	A broken wire inside the insulation.

•	Corrosion of electrical connections, splices, or terminals.

Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.

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 OBD System Check 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 for the correct function of the EVAP canister purge solenoid valve.

This step checks whether a fuel tank pressure sensor malfunction is present. The input signal voltage of the fuel tank pressure sensor should indicate atmospheric pressure, 3.0 to 3.6 volts, with the fuel tank filler cap removed. The fuel tank pressure sensor voltage will vary with atmospheric pressure. A typical voltage at sea level is 3.2-3.3 volts.

This step checks for a possible leak in the EVAP system from the fuel tank to the fuel tank pressure sensor. Normal operation of the EVAP canister prevents EVAP system pressure from exceeding 3.3 mm Hg (6.0 in H2O). 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.

When the EVAP pressure switching solenoid turns ON, fuel tank vapor pressure is applied to the fuel tank pressure sensor thru the EVAP canister. Turning ON the EVAP pressure switching solenoid while pressurizing the fuel tank should cause the fuel tank pressure sensor voltage to increase.

This step checks for EVAP system leaks. By connecting the EVAP canister purge solenoid hose and the EVAP vapor line together, the fuel tank, the fuel filler hose assembly, and the EVAP purge line can be pressurized and checked for leaks. Be sure to check all connections and sealing points for leaks.

This step checks for the correct function of the EVAP pressure switching solenoid.

This step checks for a condition that causes fuel vapor pressure to remain trapped at the fuel tank pressure sensor.

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 the malfunction that caused the DTC P0446 is still present. Operating the vehicle in check mode enhances the PCM's diagnostic capabilities. The EVAP Purge diagnostic can be monitored on the scan tool under the MIL/System Status selection of System Information. When the EVAP Purge test displays a YES status (indicating that the purge system diagnostic is completed) check for a DTC P0446 in the Last Test Failed screen of the scan tool. If there is no DTC P0446 displayed the EVAP purge system diagnostic has run and passed, indicating that no malfunction was present this time. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the system diagnostics being performed. Do not forget that the MIL/System Status 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. For additional information on check mode operation refer to Powertrain Control Module Diagnosis.

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

Step

Action

Value(s)

Yes

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Install a scan tool.
Check for DTCs.

Is a DTC P0450 present?

Go to DTC P0450 Fuel Tank Pressure Sensor Circuit

Go to Step 3

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

•	The EVAP canister purge solenoid valve

•	The fuel tank pressure sensor

•	The EVAP pressure switching solenoid

•	The EVAP canister

•	The EVAP system lines, hoses, and fittings

Repair as necessary.

Was repair necessary?