2002 Chevy Silverado 4.8L with a P0449 EVAP system Vent Control Circuit Low trouble code. The vent solenoid on every EVAP system is a normally open solenoid. When the computer performs a leak test, it will close this solenoid. A common problem on GM EVAP vent solenoids is they will stick open and cause EVAP large leak codes. In this particular case we are dealing strictly with an electrical system fault. The information contained in this video will apply to all ground side switched computer controlled devices (solenoids, relays, motors etc) There were three separate codes on this truck. Here are the videos for the other two codes.

How to test a fuel gauge P0463 (thermistor circuit design) - GM

How to troubleshoot an EVAP Pressure Sensor problem P0452 - GM

Engine Performance Diagnostics chapter 3

symptoms 50

  • check engine light (P0449 fault code)

fix 50

  • replace vent solenoid (open solenoid winding)

test shown enh 50

  • how to test an EVAP vent solenoid
  • how to determine power or ground side switching
  • how to perform a circuit integrity test
  • how to identify circuit design on a wiring diagram
  • theory an operation of the computer circuitry used to control the vent solenoid
  • how to test the computer transistor driver
  • how to command the computer to turn on the vent solenoid

Tools used

  • scan tool (bi-directional type)
  • incandescent test light
  • digital multimeter
  • back-probing tools

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(Chapter 3) Transistors, Solenoids, Computer Controlled Output Testing

Related videos:

EVAP leak P0455 (vacuum cut valve-bypass valve test) - Nissan:


How to test an EVAP Vent solenoid (applies to all cars) - GM:


2008 Chevy Avalanche EVAP Vent Solenoid Test (P0449, P0455):


EVAP Leak Test P0455:


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For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available as an eBook or paper book.

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