How To Test The EVAP Vent Solenoid (1999-2002 V8 Chevrolet Silverado, GMC Sierra)

TEST 2: Making Sure The EVAP Solenoid Is Allowing Fresh Air Intake

Before we bench test the EVAP vent solenoid, we need to make sure that it's in an OFF state and allowing fresh air intake.

To accomplish this test, you'll remove the EVAP vent solenoid from its spot underneath the pickup's bed and blow air into its fresh air outlet port (see photo above).

If all is OK with the vent solenoid, the air will enter the outlet port and pass unobstructed to the other side of the solenoid's air filter canister.

You can use compressed air or you can use your mouth to blow air into the EVAP vent solenoid.

OK, let's get testing:

1. 1

   Disconnect the EVAP vent solenoid from its connector.

2. 2

   Remove the EVAP vent solenoid from its place.
   
   This is done by removing the bolt from the solenoid's mounting bracket.

3. 3

   Disconnect the plastic line that connects the EVAP vent solenoid to the EVAP carbon canister.
   
   This plastic line is the one that connects to the EVAP vent solenoid's fresh air outlet port.
   
   Your EVAP vent solenoid should look like the one in the photo above.

4. 4

   Blow air into the vent solenoid's fresh air outlet port.
   
   I usually clean the fresh air outlet port and use my mouth for this step.

5. 5

   Air should easily pass thru' the EVAP vent solenoid.

Let's take a look at what your test results mean:

CASE 1: Air passed thru' the EVAP vent solenoid. This is the correct and expected test result.

The next step is to bench-test the EVAP vent solenoid. For this test go to: TEST 3: Bench Testing The EVAP Vent Solenoid.

CASE 2: Air DID NOT pass thru' the EVAP vent solenoid. This result tells you that the vent solenoid is either obstructed (internally) or is bad and is stuck in its closed state.

Your next step is to use compressed air to clean the EVAP vent solenoid. Go to: Cleaning The EVAP Vent Solenoid.

TEST 3: Bench Testing The EVAP Vent Solenoid

Now that you've made sure that the EVAP vent solenoid is getting power and it's allowing air to pass thru' it, the next step is to bench-test it.

This simply involves applying 12 Volts and Ground, from your Chevrolet Silverado or GMC Sierra's battery, with jumper wires.

To avoid shorting the jumper wires together, when applying battery voltage and Ground to the solenoid, I recommend that you use jumper wires with insulated alligator clips.

You can see an example of jumper wires with insulated alligator clips in photo 2 of 2 in the image viewer above.

OK, let's get this show on the road:

1. 1

   Connect the red insulated jumper wire to the male terminal labeled with the letter B in the photo above.

2. 2

   Connect the other end of the red jumper wire to the battery positive (+) terminal.

3. 3

   Connect the insulated black jumper wire to the male terminal labeled with the letter A.

4. 4

   Connect the other end of the black jumper wire to the battery negative (-) terminal.

5. 5

   The EVAP solenoid should make a 'click' sound as soon as you apply Ground to it.
   
   With 12 Volts and Ground applied to the EVAP vent solenoid, the solenoid should be closed and should not allow any air to pass thru' it.

6. 6

   Blow air into the air outlet port of the solenoid (you can use your mouth) to make sure that the solenoid has closed and is NOT allowing air to pass thru' it.

7. 7

   Air should not be able to be blown across the EVAP vent solenoid.

Let's take a look at what your test results mean:

CASE 1: The vent solenoid activated and did not allow air to pass thru' it. This is the correct and expected test result.

You can conclude that the EVAP vent solenoid is good if you have:

• Confirmed that the EVAP solenoid is getting 10 to 12 Volts (TEST 1).
• Confirmed that you can easily blow air thru' the EVAP vent solenoid in its OFF state (TEST 2).
• Confirmed in this test section that the EVAP vent solenoid closes and blocks air going thru' it when you applied 12 Volts and Ground to it.

CASE 2: The vent solenoid activated but still allowed air to pass thru' it. This test result lets you know that the EVAP vent solenoid is bad and needs to be replaced.

CASE 3: The vent solenoid DID NOT activate and still allowed air to pass thru' it. This test result lets you know that the EVAP vent solenoid is bad and needs to be replaced.