Carbon canister solenoid valve

The purpose of this test is to evaluate the correct operation of the carbon canister solenoid based on the switching voltage during engine hot run conditions. 

Connection guidance

Connection for diagnostic work will vary dependent on application.

Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.

General connection advice:

PicoScope offers a range of options within the test kits.

Dependent on difficulty of access, choose from

  1. Breakout leads.
  2. Back-pinning probes.

Testing sensors and actuators (to include relevant circuit/connectors):

  • When testing a sensor, it is desirable to gain access at the control module.
  • When testing an actuator, it is desirable to gain access at the actuator.

How to perform the test

  1. Use the vehicle wiring diagram to identify the return/signal circuit.
    Note, the canister is operated by the ECM using switched earth Pulse Width Modulation (PWM). There will be supply voltage at both terminals until the canister begins to operate.
  2. Connect PicoScope Channel A to the vehicle.
  3. Start and run the engine up to normal operating temperature.
  4. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  5. Select GO  or press the space bar to see live data.
  6. With your live waveform on screen select STOP or press the space bar to stop your capture.
  7. Turn off the engine.
  8. Use the WAVEFORM BUFFER and ZOOM tools to examine your waveform.

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 solenoid type.

The 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 V supply and its switching can be seen in the example waveform.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, Carbon Canister purge solenoid voltage.

Example Carbon Canister Solenoid.

Further guidance

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 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 the hydrocarbon vapour through the cut off valve into the inlet manifold.

GT030-2

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

  • Premium 6-way breakout lead set

    £269.00

  • Back-pinning Probe Set

    £40.00

  • Flexible Back-pinning Probe

    £3.00

  • PicoScope Battery Clip

    £2.75

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Guided test: Carbon Canister Solenoid Valve