2001 BLAZER 4DR 4WD LT CODES 449 & 452 WILL NOT CLEAR. I used an innova 3000a and clear the codes but they come right back in the INNOVA screen.

I would suspect a short , I have changed the fuel pressure sensor switch on top of the tank and the fuel cap couldn't be an issue at all since the codes never clear. It has to be a short or signal issue is my guess ?

I have disconnected the battery & pulled the ecbm & any other fuses related as wells as swapped the fuel pump relay.

I did check the vacuum lines and found & fixed a broken hose, but it went to a small valve near the wiper motor.

But even vacuum lines can't make the codes not clear. It clears the service engine light briefly until the key is on again.

I CHANGED THE VENT valve under the spare tire & no luck there either . Since a had a similar issue with an 01 malibu I found a shorted O2 sensor when it let out the majic smoke and it had 3 or 4 emissions codes until ai FIXED THE O2 SENSOR. Also changed the gas cap .

SO I disconnected one sensor at a time and no luck there either .
By eliminating the O2 sensors by disconnecting them it could still be the wires somewhere

PLEASE HELP if you have info thanks

 

P0449 - EVAP Canister Vent Solenoid Valve Control Circuit
P0452 - Evaporative Emission Control System Pressure Sensor Low Input

Here is the first thread that pops up by typing 'P0449' in the handy search function:
https://blazerforum.com/forum/2nd-generation-s-series-1995-2005-tech-41/p0449-p0453-27473/

Have you tested for voltage/ground at each of these items prior to replacing them?

 

CODES 449 & 452 will not clear yet, My handheld INNOVA 3100A clears the service eng. light only , the codes still show in the handlheld always, which leads me to believe it is not lines, caps or the canister.
The canister alone could not create the code and keep it when the truck isn't running.

There is no ground/s for either the canister , not the vent valve above the spare. THE CANISTER does not have any wiring to it and the vent valve only has a signal and return wires according to how it is supposed to function.

I have disconnected to eliminate all valves , sensors and replaced all questionable vacuum lines.

 

Are you sure that you are clearing active & history codes?

The valves ground by/through the PCM power is constant from the ENG 1 fuse. A continuity test from the valves to the proper pin in the PCM should tell you whether the wiring is good or not for the ground side.

 

449 & 452 codes don't erase & only temp clear CEL til next start. I looked for grounds anyway and found two that meet up on the frame above the EVAP VENT valve cleaned and brushed the area & reconnected grounds , I DON'T HAVE A PCM wiring schematic, but wish I DID.

I also found the idle too low at 600 & raised it to 750. Now the CEL isn't coming right back on each new start. But after 449 & 452 erase & clear the CEL they automatically come back into my scanner screen as if not cleared. This is why I'd say something is shorted or causing these codes like my Malibu when it turned out to a shorted O2 sensor.

Funny thing then It almost never showed an 02 sensor code.

 

ORDERED A BRAND NEW VENT VALVE from GM partsgiant and put a whole can of seafoam in the gas in case the vapors are somehow related its supposed to help pass emissions tests. I'm going to try & read the voltage coming back from the vent valve that's in it