GM Malibu/Cutlass 1997-2000

Evaporative Emission Controls

Print

OPERATION





Click image to see an enlarged view

Fig. EVAP system schematic-2.4L engine shown



Click image to see an enlarged view

Fig. Location of the EVAP canister hose connections

Changes in atmospheric temperature cause fuel tanks to breathe, that is, the air within the tank expands and contracts with outside temperature changes. If an unsealed system was used, when the temperature rises, air would escape through the tank vent tube or the vent in the tank cap. The air which escapes contains gasoline vapors.

The Evaporative Emission Control (EVAP) System provides a sealed fuel system with the capability to store and condense fuel vapors. When the fuel evaporates in the fuel tank, the vapor passes through the pressure control valve, through vent hoses or tubes to a carbon filled evaporative canister. When the engine is operating, and at normal operating temperature, the vapors are drawn into the intake manifold and burned during combustion.

A sealed, maintenance free evaporative canister is used. The canister is filled with granules of an activated carbon mixture. Fuel vapors entering the canister are absorbed by the charcoal granules. A vent cap is located on the top of the canister to provide fresh air to the canister when it is being purged. The vent cap opens to provide fresh air into the canister, which circulates through the charcoal, releasing trapped vapors and carrying them to the engine to be burned.

Fuel tank pressure vents fuel vapors into the canister. They are held in the canister until they can be drawn into the intake manifold. The canister purge valve allows the canister to be purged at a pre-determined time and engine operating conditions.

The fuel tank is sealed with a pressure-vacuum relief filler cap. The relief valve in the cap is a safety feature, preventing excessive pressure or vacuum in the fuel tank. If the cap is malfunctioning, and needs to be replaced, ensure that the replacement is the identical cap to ensure correct system operation.

COMPONENT TESTING



The EVAP and enhanced EVAP system monitor is incorporated in the OBD-II engine control system. A pressure sensor is mounted on the fuel tank which measures pressure inside the tank, and a purge flow sensor measures the flow of the gases from the canister into the engine. The vent valve for the canister is now controlled by the Powertrain Control Module (PCM). It performs the same functions as the purge valve, however it looks slightly different. A canister vent solenoid is mounted on the canister, taking the place of the vent cap, providing a source of fresh air to the canister.

The PCM can store trouble codes for EVAP system performance; a list of the codes is provided later in this section.

As part of the OBD-II diagnostic system, a test port is installed in the purge line connecting the purge solenoid to the canister. This test port is used to connect a special tester that pressurizes the EVAP system and measures the leakage rate. This tool is very expensive and requires training to operate or you could do damage to the vehicle, however, many professional shops have this device. If you suspect a leak in your EVAP system, you may want to consult a professional shop about performing this test on your car.

A visual inspection is one of the best checks of a EVAP or enhanced EVAP system operation, check for the following conditions:

  1. Poor connection at the PCM. Inspect the PCM harness connectors for backed out terminals, improper or loose connections, broken clips or locks, damaged or corroded terminals, and poor terminal to wire connection.
  2.  
  3. Inspect the wiring harness for damage.
  4.  
  5. Inspect for incorrect purge or vacuum source line routing.
  6.  

2.4L Engine
EVAP SYSTEM

The PCM constantly checks the evaporative emissions by applying vacuum to the EVAP and monitoring for vacuum decay. The PCM monitors the vacuum level through the fuel tank vapor pressure sensor signal At an appropriate time, the EVAP canister purge valve and the EVAP vent solenoid are turned ON, allowing the engine to draw a small vacuum on the entire evaporative emission system.

After the desired vacuum level has been achieved, the EVAP canister purge valve is turned OFF, sealing the system. A leak is detected by monitoring for a decrease in vacuum level over a given time period, when all other variables remain constant. A leak blockage or faulty component in the system will cause a Diagnostic Trouble Code (DTC) to set. Refer to the procedures for pulling and reading DTC's later in this section.

3.1L Engine
ENHANCED EVAP SYSTEM

The EVAP purge solenoid valve allows manifold vacuum to purge the canister. The PCM supplies a ground to energize the EVAP purge solenoid valve (purge on). The EVAP purge solenoid is Pulse Width Modulated (PWM) or turned on and off several times per second. The PCM controlled PWM out put is commanded when the appropriate conditions have been met:



Engine coolant temperature is above 77°F (25°C).
 
After the engine has been running about 2 1 / 2 minutes on a cold start or 30 seconds in on a warm start.
 
The vehicle is operating in closed loop fuel control.
 

The evaporative leak detection diagnostic strategy is based on the PCM applying vacuum to the EVAP system and monitoring decay. A leak is detected by monitoring for a decrease in vacuum level over a given time period, when all other variables remain constant. A leak blockage or faulty component in the system will cause a Diagnostic Trouble Code (DTC) to set. Refer to the procedures for pulling and reading DTCs later in this section.

REMOVAL & INSTALLATION



EVAP Canister

Refer to of this guide for EVAP canister removal and installation.

EVAP Canister Purge Solenoid Valve
2.4L ENGINE


Click image to see an enlarged view

Fig. Disconnect the hoses (2, and 3) from the EVAP purge valve (1)

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the purge valve electrical connector.
  4.  
  5. Remove the hoses from the purge valve.
  6.  
  7. Remove the purge valve from the mounting bracket.
  8.  
  9. If replacing the bracket:
    1. Remove the purge valve mounting bracket attaching nut.
    2.  
    3. Remove the purge valve mounting bracket.
    4.  

  10.  

To install:

  1. If removed, install the mounting bracket and attaching nut. Tighten the nut to 71 inch lbs. (8 Nm).
  2.  
  3. Slide the purge valve onto mounting bracket.
  4.  
  5. Connect the hoses to the purge valve.
  6.  
  7. Attach the purge valve electrical connector.
  8.  
  9. Connect the negative battery cable.
  10.  

3.1L ENGINE


Click image to see an enlarged view

Fig. Label and detach the hoses and electrical connector from the EVAP purge solenoid valve

  1. Disconnect the negative battery cable.
  2.  
  3. Label and detach the hoses and electrical connector from the EVAP purge solenoid valve.
  4.  
  5. Release the lock tab on the solenoid mounting bracket.
  6.  
  7. Remove the EVAP purge solenoid valve.
  8.  

To install:

  1. Bend the tab on the mounting bracket to retain the EVAP purge solenoid valve.
  2.  
  3. Install the solenoid valve to the mounting bracket. Pull on the solenoid valve to ensure that it is secure.
  4.  
  5. Attach the electrical connector and hoses to the solenoid valve.
  6.  
  7. Connect the negative battery cable.
  8.  

EVAP Vent Valve
2.4L ENGINE


Click image to see an enlarged view

Fig. Unplug the EVAP vent solenoid valve electrical connector

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the vent solenoid valve electrical connector.
  4.  
  5. Loosen the vent solenoid hose clamp and remove the hose from the vent solenoid.
  6.  
  7. Unfasten the vent solenoid attaching bolt, then remove the vent solenoid from the mounting bracket.
  8.  

To install:

  1. Slide the vent solenoid onto the mounting bracket.
  2.  
  3. Install the vent solenoid and mounting bracket attaching bolt.
  4.  
  5. Lubricate the hose ends with a suitable lubricant such as liquid soap.
  6.  
  7. Install the hose to the vent solenoid and tighten the vent solenoid hose clamp.
  8.  
  9. Attach the vent solenoid valve electrical connector.
  10.  
  11. Connect the negative battery cable.
  12.  

3.1L ENGINE


Click image to see an enlarged view

Fig. Exploded view of the EVAP vent solenoid valve, bracket, and vent hose

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the vent valve electrical connector.
  4.  
  5. Remove the EVAP vent solenoid from the bracket
  6.  
  7. Disconnect the vent hose from the solenoid.
  8.  
  9. Remove the EVAP vent solenoid valve from the vehicle.
  10.  

To install:

  1. Install the EVAP vent solenoid valve.
  2.  
  3. Connect the vent hose. The canister vent hose should be routed below the fuel tank fill and vent hoses.
  4.  
  5. Attach the electrical connector.
  6.  
  7. Install the EVAP vent solenoid retaining screw.
  8.  
  9. Connect the negative battery cable.
  10.  

 
label.common.footer.alt.autozoneLogo