Purge valve (page 3 of 3)

Canister Vent Solenoid (CVS) unit – (OBD vehicles with vacuum type, fuel evaporation leak detection system only)

Figure 17

1.CVS unit 2.Mounting bracket 3.Spring clips to pipe from EVAP canister 4.Harness connector

The canister vent solenoid (CVS) valve is normally open, allowing any build up of air pressure within the evaporation system to escape, whilst retaining the environmentally harmful hydrocarbons in the EVAP canister. When the ECM is required to run a fuel system test, the CVS valve is closed to seal the system. The ECM is then able to measure the pressure in the fuel evaporative system using the fuel tank pressure sensor.

The ECM performs electrical integrity checks on the CVS valve to determine wiring or power supply faults. The ECM can also detect a valve blockage if the signal from the fuel tank pressure sensor indicates a depressurising fuel tank while the CVS valve should be open to atmosphere.

The following failure modes are possible:

• Connector or harness wiring fault (open or short circuit)
• Valve stuck open or shut
• Valve blocked

If the CVS valve malfunctions, the following fault codes may be stored in the ECM diagnostic memory, which can be retrieved using 'Testbook':