Evaporative Emission Control System Description. Pontiac Firebird 2001

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 2001 🢒 Firebird 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 Evaporative Emission Control System Description


(1)	Purge Line
(2)	Vapor From Fuel Tank
(3)	Air

The Evaporative Emission (EVAP) Control system used on all vehicles is the charcoal canister storage method. This method transfers fuel vapor from the fuel tank to an activated carbon storage canister in order to hold the vapors when the vehicle is not operating. When the engine is operating, the fuel vapor is purged from the carbon element by intake air flow, and consumed in the normal combustion process.

EVAP Canister


(1)	Purge Tube to Solenoid
(2)	Buffer Tube
(3)	Charcoal Bed
(4)	EVAP Charcoal Canister
(5)	Volume Compensator
(6)	Fresh Air Inlet from Air Separator
(7)	Liquid Fuel Trap
(8)	Vapor Tube from Fuel Tank

EVAP System

The evaporative system includes the following components:

•	The fuel tank

•	The evaporative emission canister vent solenoid

•	The fuel tank pressure sensor

•	The fuel pipes and the hoses

•	The vapor lines

•	The fuel cap

•	The evaporative emission canister

•	The purge lines

•	The purge valve solenoid

EVAP System Operation

The EVAP purge solenoid valve allows the manifold vacuum to purge the canister. The Powertrain Control Module (PCM) supplies a ground in order to energize, or purge on, the EVAP purge solenoid valve. The EVAP purge solenoid control is pulse width modulated (PWM), or turned on and off several times per second.

The EVAP canister purge PWM duty cycle varies according to the operating conditions determined by the mass air flow, the fuel trim, the engine coolant temperature, and the intake air temperature . For certain EVAP tests, the diagnostic will be disabled if the TP angle increases to more than 75 percent.

The evaporative leak detection diagnostic strategy is based on applying vacuum to the EVAP system, and monitoring for vacuum decay.

The fuel level sensor input to the PCM is used to determine if the fuel level in the tank is correct to run the EVAP diagnostic tests. To ensure sufficient volume in the tank to begin the various diagnostic tests, the fuel level must be between 15-85 percent.

The PCM monitors the fuel tank pressure or vacuum level via the fuel tank pressure sensor input.

Results of Incorrect Operation

•	Poor idle, stalling, and poor driveability can be caused by the following conditions:

-	A malfunctioning purge solenoid

-	A damaged canister

-	Hoses or lines that are split, cracked and/or incorrectly connected

•	Fuel loss or fuel vapor odor can be caused by the following conditions:

-	Liquid fuel leaking from the fuel lines

-	A cracked or damaged canister

-	An inoperative canister control valve

-	Vacuum hoses that are:

-	Disconnected

-	Mis-routed

Kinked

-	Deteriorated

Damaged

Fuel Tank Assembly with EVAP Canister


(1)	Fuel Sender Assembly
(2)	Hose (EVAP Canister to Vent Solenoid)
(3)	EVAP Vent Valve
(4)	Fuel Tank Harness
(5)	EVAP Canister
(6)	Fuel Tank
(7)	Overpressure Relief Valve
(8)	Fuel Tank Pressure Sensor

The evaporative leak detection diagnostic strategy is based on applying vacuum to the EVAP system and monitoring the vacuum decay.

The PCM monitors the vacuum level via the fuel tank pressure sensor input. At an appropriate time, the EVAP purge solenoid and the EVAP vent solenoid are turned on, allowing engine vacuum to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, the EVAP purge solenoid is turned off, sealing the system. A leak is detected by monitoring for a decrease in the vacuum level during a specific time period, with all other variables remaining constant. A small leak in the system causes DTC P0442 to be set.

If the desired vacuum level cannot be achieved in the test described above, a large leak or a faulty EVAP purge solenoid is indicated. This condition can be caused by the following conditions:

•	A disconnected or faulty fuel tank pressure sensor

•	A missing or faulty fuel cap

•	A disconnected, damaged, pinched, or blocked EVAP purge line

•	A disconnected or damaged EVAP vent hose

•	A disconnected, damaged, pinched, or blocked fuel tank vapor line

•	A disconnected or faulty EVAP canister solenoid

•	A disconnected or faulty EVAP vent solenoid

•	An open ignition feed circuit to the EVAP vent or to the purge solenoid

•	A damaged EVAP canister

Any of the above conditions will set DTC P0440.

A restricted or blocked EVAP canister vent path is detected by drawing vacuum into the EVAP system. The PCM turns off the EVAP vent solenoid and the EVAP purge solenoid, with the EVAP vent solenoid Open, and with the EVAP purge PWM at 0 percent. The PCM monitors the fuel tank pressure sensor input. With the EVAP vent solenoid open, any vacuum in the system should decrease quickly unless the vent is blocked. The following conditions cause a blockage:

•	A faulty or stuck closed EVAP vent solenoid

•	A plugged, kinked, or pinched vent hose

•	A shorted EVAP vent solenoid driver circuit

•	A plugged evaporative canister

If any of the above conditions are present, DTC P0446 sets.

The PCM checks for conditions that cause the EVAP system to purge continuously by commanding the EVAP vent solenoid on and by commanding the EVAP purge solenoid off , with the EVAP vent solenoid CLOSED, and the EVAP purge PWM at 0 percent. If fuel tank pressure level increases during the test, a continuous purge flow condition is indicated. This condition can be caused by the following conditions:

•	A leaking EVAP purge solenoid

•	EVAP purge lines and engine vacuum source lines that are switched at the EVAP purge solenoid

•	An EVAP purge solenoid driver circuit that is grounded

If any of the above conditions are present, DTC P1441 sets.

Refer to the appropriate DTCs for further diagnostic procedures regarding the EVAP system.

Visual Check of Evaporative Emission Canister

•	If the evaporative emission canister is racked or damaged, replace the canister.

•	If fuel is leaking from the canister, replace the canister, and check the lines and the line routing.