Carbon canister solenoid valve

You will require a PicoScope to perform this test. A list of suitable accessories can be found at the bottom of this page.

How to perform the test

Plug a BNC test lead into Channel A on the PicoScope, and place a large black Battery clip on the black (negative) plug and a Backpinning Probe on the coloured (positive) plug. Place the black Battery clip onto the battery negative terminal and probe the carbon canister solenoid valve connections with the Back-pinning Probe.

The electronic solenoid is activated by the switching the earth path to ground under specified conditions, under the control of the Engine Control Module (ECM).

The switching can be seen in the example waveform. The waveform is evident only once the engine has reached normal operating temperature, the throttle is opened and the engine's speed is raised to cruising speed.

The valve will have two connections:

  1. 12 volt supply
  2. Switched earth (note that there will be 12 V on both terminals until the right conditions are met to switch the valve)

Figure 1 shows the connection made to the carbon canister solenoid valve.

Example waveform

Waveform notes

This canister contains active charcoal or active carbon granules.

Most evaporation control systems reduce the emission of fuel vapour during the time the vehicle is idling in traffic, or parked in strong sunshine, by absorbing the vapour fumes into the carbon canister.

Once the engine is at its normal operating temperature the stored hydrocarbons are released into the inlet manifold where they become part of the combustible Air/Fuel mixture.

The control for allowing the hydrocarbons to be released into the inlet manifold through a cut-off valve can be achieved electrically or by vacuum: the operating principle is the same for both. Our example is from the electronic solenoid type.

The electronic solenoid is controlled by the Electronic Control Module (ECM) by switching the earth path to ground under specified conditions. The purge valve/carbon canister has a 12 volt supply and its switching can be seen in the example waveform.

Technical information

Fuel evaporation can be a serious source of atmospheric pollution from the hydrocarbon fuel stored within the tank. For this reason the tank has now become a sealed unit and a breather pipe allows fumes to collect within a canister, normally located in the engine compartment. This canister contains active charcoal or active carbon granules.

Most evaporation control systems reduce the emission of fuel vapour during the time the vehicle is idling in traffic, stationary or parked in strong sunshine, by absorbing the vapour fumes into the carbon canister. Once the engine is at its normal operating temperature the stored hydrocarbons are released into the inlet manifold where they become part of the combustible Air/Fuel mixture.

The control for allowing the hydrocarbons to be released into the inlet manifold through a cut-off valve can be achieved electrically or by vacuum: the operating principle is the same for both.

The electronic solenoid is controlled by the ECM. With the engine switched off or at idle there is no vacuum signal in the cut-off diaphragm chamber, so the vapour fumes in the canister are prevented from being released into the inlet manifold. With the engine running above idle there is a relatively high vacuum in the signal pipe.

This causes the vacuum cut-off valve to lift off its seat and allow fresh air to be drawn into the bottom of the canister through the central tube. The air is then spread over the bottom of the canister and rises through the canister purging (pushing out) the hydrocarbon vapour through the cut off valve into the inlet manifold.

Figure 2 shows a cross section of a carbon canister, with the vacuum valve in the closed position.

AT030-2

Disclaimer
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • Back-pinning Probe Set

    £48.00

  • PicoScope Battery Clip

    £5.00

  • Premium Test Lead: BNC to 4 mm, 3 m

    £48.00

  • Premium Test Leads: Set of four leads 3 m (TA125 - TA128)

    £179.00

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Guided test: Carbon Canister Solenoid Valve