GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Geo 🢒 1996 🢒 Metro 🢒 Engine 🢒 Engine Controls - 1.0L 🢒 Evaporative Emission Control System Operation Description

Purpose

The EVAP control system limits the fuel vapor emissions to the atmosphere. The EVAP control system transfers the fuel vapor from a sealed fuel tank to an activated carbon (charcoal) storage device (EVAP canister). The EVAP canister will store the fuel vapors until the engine is able to use them.

EVAP Control System Operation
Object Number: 1567218 Size: LF
(1)Throttle Body Injection Unit
(2)Fuel Vapor Separator
(3)Fuel Tank
(4)Fuel Tank Pressure Control Valve
(5)EVAP Canister
(6)Air
(7)Ignition Positive Voltage
(8)To PCM
(9)EVAP Canister Purge Valve
(10)EVAP Canister Surge Tank
(11)Vapor and Air

The fuel vapor generated in the fuel tank while driving or idling, passes through a tank pressure control valve and enters the EVAP canister. The EVAP canister contains a charcoal element that absorbs and stores the fuel vapor. When the engine is able to use the stored fuel vapor, the fuel vapor is purged from the carbon element by intake air flow (low intake manifold pressure) and consumed in the normal combustion process.

The EVAP canister purge valve is a powertrain control module (PCM) operated vacuum solenoid that controls the purging of the EVAP canister. The EVAP canister purge valve is mounted on the intake manifold next to the EVAP canister surge tank. The EVAP canister purge solenoid valve is turned ON by the PCM under the following conditions:

    • The engine coolant temperature is more than a specified value.
    • Engine RPM is more than a specified value.