GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1998 🢒 Corvette 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 Evaporative Emission Control System Operation Description

Object Number: 12722 Size: LH
(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 tanks to an activated carbon (charcoal) storage device (canister) to hold the vapors when the vehicle is not operating. When the engine is running, the fuel vapor is purged from the carbon element by intake air flow and consumed in the normal combustion process.

Fuel Vapor Canister

EVAP Canister
Object Number: 11795 Size: LH
(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

The Evaporative Emission (EVAP) control system uses a 1850 cc charcoal canister to absorb fuel vapors from the gas tanks.

When several conditions are met, the PCM will command the EVAP solenoid on and the vapor will flow to the canister where it is absorbed and stored by the charcoal. This allows the vapor to flow into the intake manifold for combustion.

This system has a remote mounted canister purge control solenoid valve. The PCM operates this solenoid valve to control vacuum to the canister. Under cold engine or idle conditions, the solenoid valve is closed, which prevents vacuum from being applied to the canister. The PCM activates (or opens) the solenoid valve and allows purge under the following conditions:

    • When the engine is started and coolant temperature is less than 50°C (122°F), purge will be delayed for 150 seconds.
    • When the engine is started and coolant temperature is greater than 50°C (122°F), purge will be delayed for 45 seconds.
    • Throttle angle greater than 3% to enable purge. Then, if the throttle angle drops below 2%, the purge will be disabled.
    • Engine air flow greater than 12 grams per second.
    • Vehicle speed greater than 16 km/h (10 mph) to enable purge. Then, If the vehicle speed drops below 5.0 km/h (3 mph), the purge will be disabled.

Results of Incorrect Operation
    • Poor idle, stalling and poor driveability can be caused by the following:
       - Inoperative purge solenoid valve.
       - Damaged canister.
       - Hoses split, cracked and, or not connected to the proper tubes.
    • Evidence of fuel loss or fuel vapor odor can be caused by:
       - Liquid fuel leaking from fuel lines.
       - Cracked or damaged canister.
       - Inoperative canister control valve.
       - Vacuum hoses that are:
   - Disconnected.
   - Mis-routed-routed.
   - Kinked.
   - Deteriorated or damaged vapor hoses.

If the solenoid valve is open, or is not receiving power, the canister can purge to the intake manifold at the incorrect time. This can allow extra fuel during warm-up, which can cause rough or unstable idle.

EVAP Vacuum Switch
Object Number: 65919 Size: SH

EVAP Purge Vacuum Switch

The EVAP Purge Vacuum Switch is used by the PCM to monitor EVAP canister purge solenoid operation and purge system integrity. The EVAP Purge Vacuum Switch should be closed to ground with no vacuum present (0% EVAP Purge PWM). With EVAP Purge PWM at 25% or greater, the EVAP Purge Vacuum Switch should open.

An incorrect EVAP Purge system flow should set a DTC P0441. A continuous purge condition with no purge commanded by the PCM should set a DTC P1441. Refer to Evaporative Emission (EVAP) Control System for a complete description of the EVAP system.

The Evaporative Emission (EVAP) canister purge solenoid valve and the EVAP Vacuum switch diagnosis is covered in the following DTCs:

    • P0441
    • P0443
    • P1441

Visual Check of EVAP Canister

If cracked or damaged, replace EVAP canister.