Evaporative Emission Control System Description. Cadillac Eldorado 2001

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 2001 🢒 Eldorado 🢒 Engine 🢒 Engine Controls - 4.6L 🢒 Evaporative Emission Control System Description

EVAP System Components

EVAP System Overview


(1)	EVAP Canister Purge Solenoid
(2)	EVAP Canister
(3)	Fuel Fill Neck/Fill Cap
(4)	Rollover Valve/Fuel Tank Pressure (FTP) Sensor
(5)	Fuel Tank
(6)	EVAP Canister Vent Solenoid
(7)	Vent Hose/Pipe
(8)	EVAP Vapor Pipe
(9)	EVAP Purge Pipe
(10)	EVAP Service Port

The evaporative emission (EVAP) system contains the following components:

•	The EVAP fuel vapor canister

•	The EVAP purge solenoid valve

•	The EVAP vent valve

•	The EVAP fuel tank pressure sensor

•	The fuel tank

•	The fuel vapor and vent lines

Enhanced EVAP System Operation

The EVAP control system collects the fuel vapors from the fuel tank. When the engine is not running, a canister filled with activated carbon (charcoal) stores the fuel vapors. When the engine is running, the stored fuel vapors are drawn from the canister, then mixed with the intake air flow, and consumed in the normal combustion process.

The powertrain control module (PCM) uses the EVAP purge valve to control the flow of the fuel vapors from the canister. The PCM supplies the ground to energize the EVAP purge valve (purge ON). The PCM controls the ON and OFF time of the EVAP purge valve by a pulse width modulated (PWM) signal. The PCM determines the EVAP purge valve PWM duty cycle based on certain operating conditions, such as mass air flow, engine coolant temperature, manifold absolute pressure, and intake air temperature.

Diagnosis

The PCM tests the EVAP system by applying vacuum to a sealed system, then monitoring the rate of vacuum decay. The PCM determines the vacuum decay using the signal from the fuel tank pressure sensor. The PCM tests the EVAP system for the following conditions:

•	Large and small leaks (DTC P0440 and DTC P0442)

•	Excess vacuum (DTC P0446)

•	Purge flow during non-commanded conditions (DTC P1441)

•	Fuel pressure sensor (DTC P0452, DTC P0453)

•	Fuel level sensor faults (DTC P0461, DTC P0462 and DTC P0463)

•	EVAP purge (DTC P0443) and vent valve (DTC P0449) solenoid malfunctions

The PCM tests the evaporative emission (EVAP) system when the following conditions are met:

•

No throttle position (TP) sensor, manifold absolute pressure (MAP) sensor, vehicle speed sensor (VSS), intake air temperature (IAT) sensor, engine coolant temperature (ECT) sensor, heated oxygen sensor (HO2S), fuel trim, fuel level sensor, misfire, fuel injectors, exhaust gas recirculation (EGR), pintle position, fuel tank pressure (FTP) sensor, fuel level sensor, or mass air flow (MAF) sensor DTCs are set.

•	The battery voltage is between 10-18 volts.

•	The barometric pressure (BARO) is more than 72 kPa.

•	The fuel level is steady between 15-85 percent.

At an appropriate time, the PCM turns ON the EVAP purge and EVAP vent valves. This opens the EVAP purge valve and closes the EVAP vent valve. The engine draws a small vacuum on the entire EVAP system. After achieving the desired vacuum level, the PCM turns OFF the EVAP purge valve. The PCM detects a leak by monitoring decrease in the vacuum level over a period of time. A small leak in the system causes DTC P0442 to set. A large leak, EVAP or a malfunctioning purge valve will causes an insufficient vacuum level in the system and will set DTC P0440. A large leak may be the result of the following conditions:

•	Disconnected or malfunctioning fuel tank pressure sensor

•	Missing or malfunctioning fuel cap

•	Disconnected, damaged, pinched, or blocked EVAP purge line

•	Disconnected or damaged EVAP vent hose

•	Disconnected, damaged, pinched, or blocked fuel tank vapor line

•	Disconnected or malfunctioning EVAP purge valve

•	Disconnected or malfunctioning EVAP vent valve

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

•	Damaged EVAP canister

•	Leaking fuel sender assembly O-ring

•	Leaking fuel tank or fuel filler neck

The PCM also tests the EVAP system for a restricted or blocked vent path. First, the PCM turns ON the EVAP purge and EVAP vent valves. As indicated above, this opens the EVAP purge valve and closes the EVAP vent valve. The engine draws a small vacuum on the entire EVAP system. Then, at the appropriate vacuum level, the PCM turns OFF the EVAP purge and EVAP vent valves. This closes the EVAP purge valve and opens the EVAP vent valve. At this time, the PCM monitors the vacuum decay using the signal from the fuel tank pressure sensor. Unless a blocked vent path is present, the PCM should detect a quick decay of the vacuum. DTC P0446 will set if a blocked vent path is present. DTC P0446 may be the result of the following conditions:

•	Malfunctioning EVAP vent valve (stuck closed)

•	Plugged, kinked, or pinched vent hose

•	Shorted EVAP vent valve control circuit

To check for a continuous purge condition, the PCM turns OFF the EVAP purge valve and turns ON the EVAP vent valve. This closes the EVAP purge valve and opens the EVAP vent valve. The PCM again monitors the vacuum level in the EVAP system. With the purge valve closed and the vent valve opened, the PCM should detect no vacuum in the EVAP system unless a continuous purge conditions is present. DTC P1441 will set if the PCM detects a continuous purge condition. Any of the following conditions will set DTC P1441:

•	EVAP purge valve leaking

•	EVAP purge and engine vacuum source lines switched at the valve

•	EVAP purge valve control circuit grounded