I have recently acquired a 2000 LT Blazer 4x4. The engine light recently came on and when scanned, shows a P0446 evap code. I’ve been told to check out the gas cap, which appears to be after market but clicks fine and the purge valve. The original purge valve appeared to be fine but I replaced it anyway. After a few drives, the engine light came back on with the same code. Anyone have any tips? Much appreciated. Thank you.

 

This can be many things and unfortunately complete diagnostic testing requires a high end scanner with bidirectional control. The engine computer is not getting the expected results from the fuel tank pressure sensor during an evap system test.

1. Which valve did you replace, the purge solenoid (near the engine) or the evap vent solenoid (near the charcoal cannister)?
2. Is the tank hard to fill because the fill nozzle keeps shutting off at the pump (flooded or blocked charcoal cannister??
3. Do you have a scanner that can read live data, in particular fuel tank pressure value?

If swapping parts is your thing Then it can be:

1. Fuel tank sensor or its wiring
2. 5v reference circuit/wiring
3. Evap vent solenoid/wiring
4. Purge solenoid/wiring
5. Cannister
6. Lines that are leaking or blocked
7. Gas cap
8. Engine computer

George

 

Thank you for the detailed reply. I didn't realize it could be so many issues. I answered your questions below:

1. I replaced the purge solenoid (near the engine) not the evap vent solenoid (near the charcoal canister)
2. The tank is not hard to fill
3. I do NOT have a scanner that can read live data

Perhaps my easiest route is getting it scanned on a high end scanner so I can diagnose the issue a bit. Any suggestions for that route?

 

A static high end scan will most likely not tell you much. Used to monitor the fuel tank pressure sensor value while you command the solenoids would help diagnose the problem. This can be an actual leak/blockage, solenoid problem or a sensor malfunction. In the absence of this your option is trynostics. I would go in the following sequence:

1. investigate as many evap lines as you can see for leaks/kinks
2. New gas cap
3. New evap vent solenoid
4. New FTP sensor
5. New charcoal canister

George

 

Forgot: Test FTP sensor 5v ref and signal ground

George

 

Again, thank you George for your detailed replies. You are the man. I want to make sure I am getting the right parts. Do you mind checking these links to make sure we are talking about the same things and I am not wasting too much time?

• Fuel Tank Pressure Sensor
  Fuel Tank Pressure Sensor
• Vapor Canister Vent Solenoid
• Vapor Canister

Ill check the lines as well but these parts are cheap enough I could just replace them for safe measure.

 

The FTP sensor is right but the links for the other 2 dont work

George

 

Alright how about these links?

Duralast Vapor Canister VC4113
I see that this canister has 3 rods/valves instead of 2 like the other link

Duralast Canister Vent Valve Solenoid PV157
I am not sure what differs from this one but it says it fits.

 

I can't verify that those are the exact part number for your year and model but yes those are the parts. Rock auto is a very reliable site to get the part numbers right. Don't forget a new gas cap and test the reference voltage after you pull the FTP sensor wire harness. Good luck.

George

 

Thanks George. Ill report back