The following is an partial extraction from the Info 2000 Data CDROM.

Canister purge valve

Function:

The canister purge valve forms part of the emission control system. Petrol vapor from the petrol tank that is stored in the carbon absorption filter, is conveyed to the engine through this solenoid valve.
If the lambda control of the engine is functioning, the valve is powered by the control unit. The extra fuel in form of vapor that is conveyed through this system to the engine is compensated for by the lambda control.

Electrical control:

Generally the canister purge valve is closed normally. This means that the valve breaks the connection between the intake manifold and the active carbon filter, if no current is running through the valve. The activation of the canister purge valve occurs by means of the control unit connecting the valve to ground. During this time the voltage of the terminal from the control unit that connects the canister purge valve, amounts to 0 Volt. Frequently triggering takes place with pulses. The pulse ratio (duty-cycle) then depends on engine speed, engine temperature and engine load, among other things.

Specification:

Resistance: 15 - 75 ohms
Supply voltage: 12 V
Current: 250 mA

Electrical diagnosis:

STATIC CHECK:

The canister purge valve is checked by carrying out the following steps:

DYNAMIC CHECK:

An oscilloscope is used to check the signal of a canister purge valve.


Figure 1: Example of an oscilloscope image of a ground-connected canister purge valve.
During the time that the ECU does not power the valve, the voltage amounts to 12 V.
During the time that the ECU powers the valve, the voltage amounts to 0 V.


Mechanical diagnosis:

Electude BV, The Netherlands

 

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