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I have a 2000 Blazer that is failing the state inspection.  It is giveing  3 coded P0446, P0452, P0453.  These seemd to be a evap problem.  I called auto zone and they said check the vac tubes on the canister purge valce solenoid and the canister vent valve solenoid.  ANy clues where they would be?  Any clues what else I can check?

Thanks for the help  

first is to check the wiring harness..    there have been reports of wiring harness that have fallen across the drive shafts and worn through..   this would also cause the codes..

you will want to look at the proper diagnostic charts to see what wires are involved... what voltages should be on what wire.. before you replace anything..  

evap codes sometimes require a special tester to pressurize the fuel tank to 1 PSI and hold it.. while the pressure is monitored..

if you had an advanced scan tool...  it might make this simpler..


i am hoping that you at least have a digital volt meter  they can be had for under 25 bucks..

more info is coming..  

some info on how the evap system works..

Enhanced EVAP System


The Enhanced EVAP System includes an EVAP canister, fuel tank vapor pressure (FTVP) sensor, purge and vent solenoids, a fuel level sensor, a service port and the fuel cap. The FTVP sensor is used as part of a diagnostic strategy that is based on applying vacuum to the system and then monitoring the amount of vacuum decay over time.

Once the test criteria are met, source vacuum is used to draw a small amount of vacuum on the entire system by mechanically sealing off the designed vent path. After a calibrated amount of vacuum has been achieved, the vacuum source is turned off (system is closed). Leaks are detected by testing the amount of vacuum decay over time.



Fig. Enhanced EVAP System Graphic

EVAP Purge System


This system includes an EVAP canister (with vapor lines), a purge solenoid (with purge lines), a vacuum switch, fuel tank and cap and related pipes and hoses. The vacuum switch is used to detect when the system is purging. It senses the flow of vacuum from the engine through the purge valve. It is closed when the system is purging.





EVAP System Monitor


The EVAP System Monitor is a PCM diagnostic run once per trip that monitors the Evaporative Emissions Control System in order to detect a loss of system integrity or leaks of more than 0.040" in the system.

The GM vehicles included in this section are equipped with an EVAP Purge System or an Enhanced EVAP System (1997-2002 models).

Fuel System Monitor


The Fuel System Monitor is a PCM diagnostic that continuously monitors the Fuel system to verify its ability to provide compliance with OBD II regulations. This diagnostic must fail if it detects a fault that could cause tailpipe emissions to exceed the FTP standards.




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EVAP Canister
The canister is filled with carbon pellets used to absorb and store fuel vapors. Fuel vapor is stored in the canister until the control module determines that the vapor can be consumed in the normal combustion process.

EVAP Control System
The evaporative emission (EVAP) control system limits fuel vapors from escaping into the atmosphere. Fuel tank vapors are allowed to move from the fuel tank, due to pressure in the tank, through the vapor pipe, into the EVAP canister. Carbon in the canister absorbs and stores the fuel vapors. Excess pressure is vented through the vent line and EVAP vent solenoid to atmosphere.

The EVAP canister stores the fuel vapors until the engine is able to use them. At an appropriate time, the control module will command the EVAP purge solenoid ON, open, allowing engine vacuum to be applied to the EVAP canister. With the EVAP vent solenoid OFF, open, fresh air will be drawn through the solenoid and vent line to the EVAP canister. Fresh air is drawn through the canister, pulling fuel vapors from the carbon.

The air/fuel vapor mixture continues through the EVAP purge pipe and EVAP purge solenoid into the intake manifold to be consumed during normal combustion. The control module uses several tests to determine if the EVAP system is leaking.

The EVAP system consists of the following components:

EVAP Purge Solenoid
The EVAP purge solenoid controls the flow of vapors from the EVAP system to the intake manifold. This normally closed solenoid is pulse width modulated (PWM) by the control module to precisely control the flow of fuel vapor to the engine. The solenoid will also be opened during some portions of the EVAP testing, allowing engine vacuum to enter the EVAP system.

EVAP Service Port
The EVAP service port is located in the EVAP purge pipe between the EVAP purge solenoid and the EVAP canister. The service port is identified by a green colored cap.

EVAP Vent Solenoid
The EVAP vent solenoid controls fresh airflow into the EVAP canister. The solenoid is normally open. The control module will command the solenoid closed during some EVAP tests, allowing the system to be tested for leaks.

Fuel Tank Pressure Sensor
The FTP sensor measures the difference between the pressure or vacuum in the fuel tank and outside air pressure. The control module provides a 5-volt reference and a ground to the FTP sensor. The FTP sensor provides a signal voltage back to the control module that can vary between 0.1-4.9 volts. As FTP increases, FTP sensor voltage decreases, high pressure = low voltage. As FTP decreases, FTP voltage increases, low pressure or vacuum = high voltage.  

Man, that is awesome stuff, I think I can fix this thing if I can find them. According to the drawing it looks like the canister is under the hood.  I cant find anything, the canister(I would assume is big) the valves . . .ect Where would the canister be?  I would think it would be near the front of the engine near he radiator, but I have looked and looked.  Any clues as to where theses parts are on teh vehicle?

Once again thanks for all the info!  

you are going to need the trouble shooting charts for each code..

i have looked around in the stuff i can find easily..

you are probably going to need a short subscription to alldatadiy.com or eautorepair.net

as they have the exact charts and info available to test the system..

Diagnostic Trouble Code P0446
Category Powertrain
Definition Evaporative Emission System Vent Control Circuit

Definition of Diagnostic Trouble Code P0452
Category Powertrain
Definition Evaporative Emission System Pressure Sensor/Switch Low

Definition of Diagnostic Trouble Code P0453
Category Powertrain
Definition Evaporative Emission System Pressure Sensor/Switch High


more to come...  

i am not sure this is the exact diagram.. but its probably really close..



the fuel tank pressure sensor is on the fuel pump sending unit..  on top of the tank.. with a 3 wire connector . the fuel pump and sender have 4 wires in their own plug.


i have not found a decent diagram of the component locations..

the carbon canister and some of the control valves are near the tank...
the vent control  could be at the canister or it might be the solenoid near the engine.. .

sorry.. i don't end up doing a lot of the evap codes..  like i said.. it usually involves a emission system pressure tester and more of a scan tool than i have...  so i have a friend who i send them out to..  he has racks to hoist the cars up also..