DTC P0446 Evaporative Emission (EVAP) Vent System Performance. Pontiac Firebird 1999

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 1999 🢒 Firebird 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P0446 Evaporative Emission (EVAP) Vent System Performance

EVAP Control System Overview


(1)	EVAP Vent Valve/Solenoid
(2)	EVAP Vent Valve/Solenoid Ignition Feed Circuit Terminal
(3)	EVAP Vent Valve/Solenoid Control Circuit Terminal
(4)	EVAP Vent Valve/Solenoid Filter
(5)	EVAP Vapor Lines
(6)	Fuel Tank Pressure Sensor
(7)	Fuel Tank Pressure Sensor Ground Circuit Terminal
(8)	Fuel Tank Pressure Sensor Signal Circuit Terminal
(9)	Fuel Tank Pressure Sensor Circuit 5 Volt Reference Circuit Terminal
(10)	Fuel Filler Pipe
(11)	Check Valve (Spitback)
(12)	Modular Fuel Sender Assembly
(13)	Fuel Limiter Vent Valve (FLVV)
(14)	Pressure/Vacuum Relief Valve (Optional)
(15)	EVAP Canister
(16)	EVAP Canister Purge Valve/Solenoid Ignition Feed Circuit Terminal
(17)	EVAP Canister Purge Valve/Solenoid Control Circuit Terminal
(18)	Intake Manifold Vacuum Source
(19)	EVAP Canister Purge Valve/Solenoid
(20)	EVAP Service Port

EVAP System Description

The evaporative system includes the following components:

•	The fuel tank.

•	The EVAP vent valve/solenoid.

•	The fuel tank pressure sensor.

•	The fuel pipes and hoses.

•	The fuel fill cap.

•	The EVAP vapor lines.

•	The EVAP purge lines.

•	The EVAP canister.

•	The EVAP canister purge valve/solenoid.

A RESTRICTED or BLOCKED EVAP VENT PATH is detected by monitoring fuel tank pressure during normal operation (EVAP vent valve/solenoid open, EVAP purge valve/solenoid normal). With the EVAP vent valve/solenoid open, vacuum level in the system should be very low unless the vent path is blocked. A blockage can be caused by the following conditions:

•	Faulty EVAP vent valve/solenoid (stuck closed).

•	Plugged kinked or pinched vent hose.

•	Shorted EVAP vent valve/solenoid driver circuit.

•	Plugged EVAP canister.

If any of the conditions described above are present, DTC P0446 will set.

Conditions for Running the DTC

•	No TP sensor, ODM, IAT sensor, or MAP sensor DTCs set.

•	All conditions for P0440 and P0442 have been met and passed.

•	Startup engine coolant temperature is not more than 4° C and 30° C (40° F 86°F).

•	Startup engine is not more than 8° C (14° F).

•	Startup Intake air temperature not more than 2° C and 30° C (40° F and 86° F).

•	Startup intake air temperature not more than 2° C (4°F).

•	Fuel tank level is between 15% and 85%.

•	BARO is greater than 75kPa.

Conditions for Setting the DTC

•	Fuel tank pressure is less than -10 in. H2O.

•	The condition is present for up to 30 seconds.

Action Taken When the DTC Sets

Important: Although these diagnostics are considered type A, they act like type B diagnostics under certain conditions. Whenever the EVAP diagnostics report that a system has passed, or if the battery has been disconnected, the diagnostic must fail during 2 consecuitive cold start trips before setting a DTC. The initial failure is not reported to the diagnostic executive or displayed on a scan tool. A passing system always reports to the diagnostic executive immediately.

•	The PCM will illuminate the MIL during the first trip in which the diagnostic test has been run and failed.

•	The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records data.

Conditions for Clearing the MIL/DTC

•	The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed.

•	The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

•	The DTC can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.

Diagnostic Aids

Check for the following conditions:

•	Kinked, pinched or plugged vent hose.

•	Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused 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:

The power train OBD System Check promps you to the basic checks and store the freeze frame and failure records data on the Scan Tool if applicable.

If a EVAP vent valve or EVAP purge valve electrical malfunction is present, the purge system will not operate correctly. Repairing the electrical malfunction that caused the additional DTC to set will very likely correct the condition that set this DTC.

Checks for a fuel tank pressure sensor stuck high condition. The fuel tank pressure must be relieved by removing the canister line from the fuel tank or EVAP canister. The fuel fill cap will not relieve the tank pressure due to a check valve in the filler neck. The check valve seals when pressure is applied to prevent vapor from escaping through the filler neck. The scan tool should read within +/- 1.0 in. H2O of the specified value.

Verifies that the fuel tank pressure sensor accurately reacts to EVAP system pressure changes. The EVAP station is pressurizing a sensor that normally reads vacuum. The Tech II reads high pressure at 0 Volts and high vacuum at 5 Volts. The Tech II can only read a max pressure of 6.0 in. of H2O (0 Volts). However the EVAP Service Station can pressurize the system to much higher pressures. The Scan Tool value should be within +/- 0.5 of the specified value.

Checks for a plugged or stuck closed EVAP Vent Valve/Solenoid. The value should decrease to within +/- 1.0 in. HG of the specified value.

DTC P0446 - EVAP Canister Vent Blocked

Step

Action

Value(s)

Yes

Was the Powertrain OBD System Check performed?

Go to Step 2

Go to the Powertrain On Board Diagnostic (OBD) System Check

Important: Visually/Physically inspect for the following conditions:

•	Vacuum or Purge lines disconnected. Refer to Emission Hose Routing Diagram .

•	Loose or missing fuel fill cap.

Is DTC DTC P0443 Evaporative Emission (EVAP) Purge Solenoid Control Circuit or DTC P0449 Evaporative Emission (EVAP) Vent Solenoid Control Circuit also set?

Go to the other DTC first

Go to Step 3

Ignition switch OFF.
Remove the EVAP canister line from the fuel tank or EVAP canister. This will relieve the fuel tank pressure.
Ignition Switch ON, Engine OFF.
Observe Fuel Tank Pressure on the scan tool.

Is Fuel Tank Pressure near the specified value?

0 in. H2O

Go to Step 4

Go to Step 11

Important: : Before continuing with diagnosis, zero the EVAP Pressure and Vacuum (inches of H2O gauges on the J 41413 EVAP Pressure/Purge Diagnostic Station.

Important: Do not exceed the pressure in the specified value.

Ignition Switch OFF.
Reconnect all EVAP hardware that was previously disconnected..
Install theJ 41415-40 fuel fill cap adaptor to the fuel fill neck and fuel fill cap.
Connect the EVAP station to the Fuel Tank Cap Adaptor.
Ignition Switch ON, Engine OFF.
Capture Fail Records data for DTC P0446 and clear DTCs
Using the Scan Tool, EVAP Vent Valve/Solenoid, command the Vent Valve/Solenoid On (closed) to seal the system.
Attempt to pressurize the EVAP system to the specified value by slowly turning the EVAP Service Station rotary switch to the "pressure" position (monitor the pressure with the gauge on the cart with the rotary switch in the "Off/Hold" position).
Observe Fuel Tank Pressure on the scan tool.

Is the Fuel Tank Pressure at the specified value?

5 in. H2O

Go to Step 5

Go to Step 7

Maintain EVAP pressure at the first specified (higher) value.
Command the Vent Valve/Solenoid Off (open) to relieve the pressure through the Vent Valve.

Does the EVAP pressure gauge decrease to near the Second specified (lower) value within 2 minutes with the rotary switch in the "Off/Hold" position?

5 in. H2O

0 in. H2O

Go to Diagnostic Aids

Go to Step 6

Disconnect the large vent hose (marked AIR ) from the EVAP canister.
Switch the rotary switch on the EVAP Pressure/Purge Diagnostic station to "Purge".
Start the vehicle and allow to reach operating temperature
Using the scan tool, EVAP Purge Valve/Solenoid, increase EVAP purge to 100%. The scan tool will abort the test if the vacuum is above 15 in. H2O.
Monitor the Vacuum (inches H2O) gauge on the EVAP Pressure/Purge for 5 seconds while holding the engine speed at 2,500 RPM.

Does the vacuum remain below than the specified value?

10 in. H2O

Go to Step 7

Go to Step 9

Inspect the vent hose between the EVAP canister and the EVAP vent valve/solenoid for being kinked, pinched, or otherwise blocked.
If a problem is found, repair as necessary.

Was a problem found?

Go to Step 12

Go to Step 8

Replace the EVAP vent valve. Refer to Evaporative Emission Vent Valve Replacement .

Is the action complete?

Go to Step 12

Replace the EVAP canister. Refer to Evaporative Emission Canister Purge Solenoid Valve Replacement .

Is the action complete?

Go to Step 12

Check for a kinked or restricted canister purge line between the EVAP canister purge valve and EVAP canister.
Repair the canister purge line as necessary.

Is action complete?

0 in. H2O

Go to Step 12

Ignition switch OFF.
Remove the EVAP canister line from the fuel tank or EVAP canister. This will relieve the fuel tank pressure.
Ignition Switch ON, Engine OFF.
Observe Fuel Tank Pressure on the scan tool.

Is Fuel Tank Pressure near the specified value?

0 in. H2O

Go to Step 10

Go to DTC P0453 Fuel Tank Pressure Sensor Circuit High Voltage

Reconnect all EVAP hardware that was previously disconnected.
Ignition Switch ON, Engine OFF.
Using the scan tool, EVAP Vent Valve/Solenoid, Command the vent Valve ON (closed) to seal the system.
Pressurize the EVAP system to the first specified (higher) value by slowly turning the EVAP Service Station Rotary Switch to the "Pressure" position. (Monitor the pressure with the gauge on the cart with the rotary switch in the "Off/Hold" position).
Command the EVAP Vent Valve/Solenoid OFF (open) to relieve the system pressure through the Vent Valve/Solenoid.

Does EVAP pressure decrease to less than the second specified (lower) value within 2 minutes with the rotary switch in the 'Off/Hold" position?

5 in. H2O

0 in. H2O

Go to Step 3

System OK